I waoke up early and I prepared to thefor school.

Wake —> woke (past tense - recounting events of the past)
Prepared to —> prepared for (You would use “prepared to” as in you prepared to do something, so prepared would be followed by an infinite verb (to ____). “Prepared for” would be used when you were getting ready for something, so “prepared for” would be followed by a noun.
The school —> school (you don’t need “the” here. I’ve also realised that you would rarely use any kind of article in front of “school”, unless you’re saying something like “the school that I go to”, or when you’re talking about schools in general (a school). “The” would be more common than “a” though. For example “I go to school” or “I learnt about ____ at school” instead of “I go to the school” or “I learnt about _____ at the school”.
Just a note but you can use “learned” instead of “learnt” depending on if you use American or British English)

The first class was mathematics, where we learned about fractions and how simplification.¶
OR ¶
The first class was mathematics, where we learned about fractions and how to simplify.

“Simplification” refers to the process of it, but I will say that it isn’t really used that much. The sentence with “how to simplify” would definitely be more common.

Although at first it was a little difficult, with the explicanation of the teacher, I achievedwas able to understand (it) better.

The first “it” is required - it would act like the subject here and kind of adds details about what was difficult (in the sense that it specifies that the fractions and simplifying from the previous sentence was difficult, instead of some random thing).
Explication would be a fake friend (it sounds similar to the word you want to say in your native language but means a completely different thing). In English, it refers to an analysis of some sort (but honestly it’s rarely used). “Explanation” would be the word that you’re looking for

Afterwards, we had a breake and I played soccer with my friends, so it was very funny.

“After we had a break” makes it sound like the next thing that you say happened following a break.
“Funny” means that something is amusing, like how a joke is funny because it makes you laugh. “Fun” is used when something is enjoyable or entertaining, and you like it.

ToIn the afternoon, we had class of science and literature.

You would always say “in the afternoon” instead of “to the afternoon” or “on the afternoon”. It isn’t really necessary to say “class” since the context of a school has been provided, and people would naturally assume that when you say science and literature, you mean science class and literature class.

In the class of sciencescience (class), we did an experiment about the density of the liquids, so I seemsewhich I found very interesting.

It would sound more natural to say “science class” instead of “class of science”, although I myself usually only say “science” instead of “science class”.
“The” isn’t really necessary before “liquids”.
“So I seemed very interesting” implies that other people would assume that you are interesting. “So” also means that because of the previous statement, you found it interesting, which doesn’t make much sense to say here since you didn’t say anything about enjoying science or science experiments.

In literature, we readed a chapter ofin a fascinanting book and we argued about to the character and the plot.

Past tense of “read” is still spelt “read”, but it’s pronounced in the same way as “red”. So to figure out which is which, you would need to look at the context that it’s in.
I usually say “chapter in a book” instead of “chapter of a book”, but both make sense.
No need to say “to” when talking about arguing about something.

When I geot home, I did my homework, had dinnered with my family, afternd afterwards I read a little before I sleept.

Get —> got (past tense of “get” is “got”)
Dinnered —> had dinner (there’s no word for eating specific meals, so you would say “had dinner”, “had breakfast” or something else depending on which meal you’re talking about. The closest thing there is to “dinnered” is “dined”, but it’s mainly used in really formal situations, particularly when you go out to have dinner)
After I read a little —> afterwards I read a little (“After I read a little” implies that you did something after reading. If you wanted to use that then you would say “and after I read a little I slept”, or you could start a new sentence and delete the “and”.)
Sleep —> I slept (you could say “sleeping” as well as “I slept”, but not sleep” by itself)

WIt was a large dayong but satisfying day.

You need the subject “it” here.
You would never use something related to size like “large” to describe a day. Instead you would use something to describe the length of the day, like “long”.
It would be more natural to put “but satisfying” in front of day.

I waoke up early, and I prepared to thego to school.

You're writing this in the past tense, so use the past tense of the verb, wake, which is woke to keep things consistent. I also rephrased the second part of the sentence to sound more natural.

The first class was mathematics, where we learned about fractions and how to simplificationy them.

You can also say, "I first had mathematics, where I learned about fractions and how to simplify them," if you want to write from your own perspective.

Although at first was a little difficult, with the explication of the teacher, I achieved understand better.fractions were difficult to understand at first, I grasped this concept thanks to my teacher's explanation.

I'm assuming that you're talking about how fractions were difficult to understand at the beginning of the lesson.

After math class, we had a breake and I played soccer with my friends, so was very funny../ After my math class, we had a break where I played soccer with my friends.¶

I'm unsure what you found funny. I also made your sentence more concise and readable.

ToIn the afternoon, we had class ofes in science and literature./In the afternoon, we took our classes in science and literature.

In the class of science, we diour science class, we conducted an experiment about the density of the liquids, so Iwhich seemsed very interesting.

In our literature class, we readed a chapter of a fascinanting book, and we argued about to the character and the plot.

What book did you read for context?

When I geot home, I did my homework, and had dinnered with my family, a. Afterward, I read a little before going to sleep.

WIt was a large day butbusy and satisfying day./It was an eventful and satisfying day.

Glad to hear!

My new textentry

I waoke up early and I prepared to thego to school.

TheMy first class was mathematics, where we learned about fractions and how simplification.

Although at firsit was a little difficult, with the explication of the teacher, I achieved at first, I was able to understand it better with the teacher's explanation.

After that, we had a breake and I played soccer with my friends, so it was verya lot of funny.

ToIn the afternoon, we had class of science and literature classes.

In thscience class of science, we did a experiment abouton the density of the liquids, so I seemsedwas very interestinged.

In literature class, we readed a chapter of a fascinanting book and we argued about todiscussed the characters and the plot.

When I geot home, I did my homework, ate dinnered with my family, after Ind read a little before sleepbed.

WIt was a large dayong but satisfying day.