Text types is generalized in two kinds; fiction and no-fiction. Fiction will be close relating to literature while non-fiction is deal more in technical usage of daily life.
Browsing over the Internet, I find a very useful source to learn text types in non-fiction summary. They are:
1. Report text, this kind of text is to describe the way things are, give detail description as they are
2. Procedure, this instructional text is to instruct or describe how to make something or how something is done through a series of sequenced steps or phases.
3. Recount, this text tries to retell events. Commonly the events happened in the past
4. Explanation, this kind of text surely explains the process involved in nature and how something works. Explanation text is composed a lot in natural phenomena.
5. Persuasion, as its word root, persuasive text tries to argue the case for a point of view and in higher point it makes to convince and persuade readers. Persuasion text is studied in two types; analytical exposition and hortatory text.
6. Discussion, a type of text which present argument and information from different points of view. Generally discussion text is accomplished with a recommendation
7. The other types of non-fiction text such as Internet material, leaflet, interview, diary, journalistic writing, biography and autobiography can be seen at lancsngfl.ac.uk

How Venus eclipse happens is best given to an example of explanation texts. Explanation text is compose to describe how something forms and why something exists and happens.
What is an explanation text and how is the explanation text composed? Explanation text is structured by the generic level of general statement and followed with sequenced explanation. To have clear understanding on the explanation text, let's see the following example of explanation text!

How Venus Eclipse Happens
On May 16, 2010, people in most regions in the world have seen a very rare natural phenomenon. It was Venus eclipse. It was very rare amazing natural event. It was reported that the Venus eclipse will seen again in the future in 2050. Do you know how this rare Venus eclipse happens?
Well, actually Venus eclipse is like Sun eclipse. Venus eclipses occurs when the position of the earth, moon and Venus is parallel. Venus planet will slowly disappear for a moment because it is covered the surface of the Moon. Venus planet seems to move to the back side of the Moon.
The moon and planets are sharing a similar apparent path in the sky. That is why, it is not unusual for the moon to appear to pass close to Venus. In fact, the moon appears somewhere near it about once a month. However, most people don’t see these events because they are visible in the evening sky only half the time, and then only for a short period after sunset. The apparent closeness varies from month to month as well.
Note: This example of explanation text about how Venus eclipse happens is arranged from beranda-jiwa.info and earthsky.org

Learning text types is presented as the main subject in English lesson for high school students. Most of the time during their time in high school, the students focus their attention to text types with each generic structure and what language used to construct the texts varying to each other. That generic structure and language features which are commonly found different from one text to another is used based on the purpose of each genres.

Text types in the three main genres which must be studied in high school specially designed for graduate competences standard (SKL) are:
NARRATION
This narrative genre includes narrative, recount, and news item. All these text types in narrative genres composed to tell and inform.
DESCRIPTION
The texts which include in descriptive genres are report, descriptive, and explanation. These text genres are written to describe. They tend to use words with describing sense and not telling
ARGUMENTATION
Argumentative genres will cover analytical exposition, hortatory exposition and discussion. These text types explore reason to answer the question "why" and "how".

To enlarge our knowledge, texts are defined into three main genres which slightly different from the above classification referring to the high school graduate competences standard. According to nationalstrategies, the tree main genres which show the text types distinctions are as follow:
1. NARRATIVE which includes adventure, mystery, science fiction, fantasy, historical fiction, contemporary fiction, dilemma stories, dialogue, myths, legends, fairy tales, and fables.
2. NON-FICTION which accommodates discussion texts, explanatory texts, instructional text, persuasion texts, non-chronological reports and recounts.
3. POETRY which refers to free verse, visual poems and structured poems.

How do seasons happen?
Seasons come to us regularly. We have probably noticed that it gets warmer in summer or dry season while it get colder in the winter or wet season. However do we know how these seasons change?

Seasons happen and change every year. This happens because the earth tilts back and forth as it goes around the sun. During the summer, the earth tilts toward the sun. It makes half of the earth hotter. this condition is what we call summer. During the other half of the year, the earth tilts away from the sun. As a result, it makes that half of the earth cooler. This cool condition is then what we call winter.

The different parts of the world have the same season at different times. In the northern half of the world , winter happens during the months of December, January and February. The regions are such North America and Europe. In the other hand, the southern half of the world have winter during the months of June, July and August.The regions are like South America and Australia. How does this difference happen? The same season happens at different times because the top and bottom halves of the earth tilt away from the sun at different times.

How Earthquakes Happen
Earthquake is one of the most destroying natural disasters. Unluckily it often happens in several regions. Recently a horrible earthquake has shaken West Sumatra. It has brought great damages. Why did it occur? Do you know how an earthquake happens?

Earthquakes are usually caused when rock underground suddenly breaks along a fault. This sudden release of energy causes the seismic waves. It make the ground shake. When two blocks of rock or two plates are rubbing against each other, they stick a little. They don't just slide smoothly. The rocks are still pushing against each other, but not moving. After a while, the rocks break because of all the pressure that's built up. When the rocks break, the earthquake occurs.

During the earthquake and afterward, the plates or blocks of rock start moving, and they continue to move until they get stuck again. The spot underground where the rock breaks is called the focus of the earthquake. The place right above the focus is called the epicenter of the earthquake.

Why Eiffel Tower was Built

If we talk about the Wonders of the World buildings, then we will see Eiffel Tower as one of them. However many of us do not know the tower’s past history on why it was build. Everything has the reasonable background, especially for the tower which is to be one of the most recognized buildings in the world.

Primarily, the Eiffel Tower was built for the World Exhibition. It was called Paris Exposition in 1889. The exhibition was organized to celebrate the 100th anniversary of the French Revolution. The purpose of building Eiffel Tower in such structure was to show to the world France’s advancement of technology and beauty. The Eiffel Tower was designed by Gustave Eiffel. It seemed that then the name of the tower was derived from the designer’s last name, “Eiffel”

Another reason on why the tower was built was for scientific progress. Although few realized it, the Eiffel Tower would become the prominent structure in terms of science and technology. Many experiment with temperature, pressure and pendulums were performed atop the unique famous building. Additionally the Eiffel Tower was used for radio transmission tower. Many experiments were conducted atop the Eiffel Tower for radio transmission advancement. Once the Eiffel Tower was proposed to be demolished but it was spared because the tower had the promising future as a radio tower.

(Simplified from http://ezinearticles.com/)

Generic Structure of Explanation Text

The best discourse on how and what is explanation text is answering the question word “how” and “why”. Such question words need detail explanation on it relates. However, explanation text is written in narrative style and not instructional. If it is written for the purpose of instruction, then the text genre will be labeled as PROCEDURE.

From the above example of explanation text, we see that it has the generic structure as follow:

• General Statement; the introduction of the passage on why the Eiffel Tower was built.

• Sequenced Explanation; this is the main element of explanation text. This explanation is explored to answer the “why” or “how” question introduced in the general statement. From the example above, the text was written to explain why, not how, the Eiffel Tower was built. Then it elaborates the reasons. First is for the show case and the second is for scientific and technological purposes.
  

How Roman Roads were Built

The system of roads for mobility has been begun early decades. It was started since the Roman Empire conquered the world. The roads in Roman era were known as the best construction.

The Romans built roads are for the purpose of mobility, especially for the army. Having the best road, the army could march from one place to another. They built the roads as straight as possible, so that the army could take the shortest route.

It is interesting to know how the roads were built, which some of them are still in use today. First, the Romans builders would clear the ground of rocks and trees. Then they dug a trench where the road was to go and filled it with big stones. Next, they put in big stones, pebbles, cement and sand which they packed down to make a firm base. After that, they added another layer of cement mixed with broken tiles. On top of that rough construction, then they put paving stones to make the flat surface. These stones were cut so that they fitted together tightly. As the finishing touch, kerb stones were put at each sides of the road to hold in the paving stones. It was also used to make a channel for the water to run away.

(Partly taken from: www.teachingideas.co.uk)

Now we are going to see the generic structure of the explanation sample above.

Every explanation text will be started with General Statement of the text. It is purposely to introduce the topic of the text. From the example above, we point that the Roman road architect is the main discussion, just seeing from the first sentences.

Chocolate starts a tree called cacao tree. This tree grows in equatorial regions, especially in place such as South America, Africa, and Indonesia. The cacao tree produces a fruit about the size of a small pine apple. In side the fruits are the tree's seeds. They are also known as coco beans.

Next, the beans are fermented for about a week, dried in the sun. After that they are shipped to the chocolate maker. The chocolate maker starts by roasting the beans to bring out the flavour. Different beans from different places have different qualities and flavour. So they are often shorted and blended to produce a distinctive mix.

The next process is winnowing. The roasted beans are winnowed to remove the meat nib of the cacao bean from its shell. Then the nibs are blended. The blended nibs are ground to make it a liquid. The liquid is called chocolate liquor. It tastes bitter.

All seeds contain some amount of fat and cacao beans are not different. However, cacao beans are half fat, which is why the ground nibs from liquid. It is pure bitter chocolate.

Note on the generic structure of this explanation sample.

Every text genre has its special purpose or social function. However if we see the generic structure point, we will get the understanding which both the explanation and procedure text have similar purposes. Both explain how to make or form something. However the procedure text will explain how to form or make something completely by instruction way. That is why most of procedure text is composed in command sentences. In the other hand, explanation text will show a knowledge about how thing is formed.

The above example of explanation text has the following generic structure:

General statement; it is a statement which says about chocolate and how it is formed

Sequenced explanation; it is a series of explanation on how chocolate is formed before we eat. First, the chocolate is coming from the cacao tree. Then it is fermented and ship to the chocolate producer. The cacao bean then are roasted and winnowed.

The sun seems to rise in the morning, crosses the sky during the day and sets at night. However the sun does not actually move around the earth. Earth's turning on its axis makes it look as if the sun is moves.
The earth makes a complete turn on its axis for 24 hours. It is called as rotation. It causes day and night. The earth also moves around the sun. It takes 365 days or a year. This process is called revolution. The revolution process causes the changes of the season

In the summer, the amount of daylight that we get is more than we get in winter. This is not because as much people think we are closer to the sun but because of the tilt of the earth.
The earth is actually closer to the sun in winter than it is in summer but you would be forgiven for thinking that this can not be true after looking out of your window on a cold and frosty morning.
It seems strange that as the earth get closer to the sun during its orbit then the amount of daylight that we get decrease. But that is the case. It is the tilt of the earth that determine the amount of daylight that we get and so the length of time that for us the sun is above the horizon.
(Taken from: www.ictteachers.co.uk)

Generic Structure Analysis
General statement; stating the phenomenon whic daylight in summer is longer than in winter.
Explanation; it is the tilt of the earth that determines the amount of daylight not the distance of the earth from the sun.
Language Feature Analysis
Focusing generic participant; daylight.
Using chronological connection; then, so, but.
Using pasive voice; you would be forgiven.
Using present tense; the earth is actually closer to the sun.