I can start talking about an Italian trilogy written by Federico Moccia: the first one is "tThree mMeters above the sSky" and the second one is "I dDesire yYou", (the third, I have never reded)n't read.

Correct grammatically but it would feel more natural to start with something like 'I would like to start by talking about'

"Three mMeters above the sSky" talks about the teenage relationship between Baby and Step, they live in Rome and their lives are toso different.

so sounds a little more natural than too

She likes studying, being fashionable and she is responsabible.

Correct but it would be better to start this sentence with the name rather than she.

Also, the story talks about the social classes differences, friendship, the first love, and different life problems.

Correct, but it would flow a little better if you changed it around to 'Also, the story talks about the differences between the social classes,'

The first book was published in 1992, and it was toso successful and for this reason it was made into a film.

Again 'so' is better here as it has a positive feeling whereas 'too' feels a little negative

Talking about "Sei Tu" (published in 2006), which is the second book, is the continuation of the story.

In the beginning, Step is in New York and he wants to return to Rome.

In a momenpart of the story, Step meets Baby in a party and they have a little affair, but he regrets this situation, and tells Gin what happened.

She doesn't forgive him, andbut he wants to win her back.

'but' feels more natural here

In my opinion, it's a nice book for teenangers ¶
Also there is a film based on this book.

I can start talking about an Italian trilogy written by Federico Moccia: the first one is "tThree mMeters aAbove the sSky" and the second one is "I dDesire yYou" (the third I have never redead).

Titles of books most of the words will have a capital letter.

"Three mMeters aAbove the sSky" talks about the teenage relationship between Baby and Step, they live in Rome and their lives are toovery different.

"too different" sounds like the are "too different" for a specific situation.

She likes studying, being fashionable and she is responsabible.

Also, tThe story also talks about the social classes differences, friendship, the first loves, and different life problems.

The book was published in 1992, and it was toovery successful and f. For this reason it was made into a film.

'very' rather than 'too'. having two 'ands' in the sentence makes it harder to read.

Talking about "Sei Tu" (published in 2006), the second book, is the continuation of the story.

'talking about' sounds odd with 'is the continuation'. So, I don't think it needs to be there. Is "I desire you" or "Sei Tu" the second book of the trilogy?

In a momeAt one point of the story, Step meets Baby inat a party and they have a little affair, but he regrets this situation, and tells Gin what happened.

She doesn't forgive him, andbut he wants to win her back.

to me 'but' feels better than and to emphasis the contrast.

In my opinion, its a nice book for teenangers ¶
Also t¶
There is also a film based on this book.

I recommend them!