Actually, II'm currently reading The Silmarillion by Tolkien.

"Actually" is a false friend! I make the same mistake in French. You have a few different options here. "I'm currently reading ..." is my preference, but you could also say "Right now, I'm reading ..."; either one is fine.

I'm a fan of The Lord of the rRings, andso for my birthday, my boyfriend giave me this book.

Most words in a title are capitalized, except for certain small connector words like "and" "or" "of" "in" etc.

"and" sounds like an odd connector to me because the two ideas are dependent on each other. Your boyfriend chose this gift because you're a fan of LOTR. "so" sounds more natural because it acknowledges the cause and effect.

It's the fFrench version, because iI don't have the level for reading it in English.

Names of languages are always capitalized in English. The pronoun "I" is also always capitalized.

And it's not easy in fFrench, so, I docan't imagine how it's hardhard it is in the original language.

Sentence 1: "I can't imagine how it's hard" means that someone's telling you that a thing is hard, and you think that sounds unlikely.
Sentence 2: "I can't imagine how hard it is" means that you think it's probably quite hard, so much that you can't imagine the upper limit of difficulty.

It's very confusing until you get used to it, but the word order is important. You also can't contract "it is" into "it's" in sentence 2, but I'm not sure how to explain why, since I'm a native speaker and never learned this as a formal rule.

It's very passionnateexciting to discover the origin of the creation of the Tolkien's world.

"origin of the creation of" sounds redundant, but I'm not sure what you meant, so I'm not sure what part to remove.

ButAnd yet, somehow, I don't rememberer the half of the names of theirhis characters.

The phrase you use to introduce this sentence should reflect what kind of comparison you want to draw between the two thoughts. Do you think that Tolkien is a great writer, and yet some parts of his writing are not engaging? Are you impressed that he can keep track of so many characters and so many aspects of the world, and marveling that it must be harder to write all of those details than to read them?

And Iit's just the begeinning of the book !

Unlike French, English doesn't put a space before punctuation marks like ? ! :

Actually, I read The Silmarillion by J.R.R. Tolkien.

"Actually" at the start like this feels a little odd since you're not correcting someone
Usually if we're talking about an author we would refer to their full name first and then on repeat mentions use only the surname

I'm a fan of The Lord of the rRings, and for my birthday, my boyfriend giave me this book.

Capitalisation for title
Past tense is required for "give" here

It's the fFrench version, because i don't have the level for read it in Englishmy level of English isn't high enough to read it.

Here you should use "to" with "read"
Rephrased to sound more natural

And it's not easy in fFrench, so, I docan't imagine how it's hardhard it is in the original language.

Here "can't" is a more natural choice than "don't"
"how it's hard" = "in what way is it hard"
"how hard it is" = "what level of difficulty is it"

It's very passionnateinteresting to discover the origin of the creation of the Tolkien's world.

"passionate" doesn't make sense in this sentence. I don't read French so maybe my choice of replacement isn't the best
No need for "the" when talking about "Tolkien's world"

Thisat man was a genius.

"That" feels like the more natural choice here

But I don't rememberer the half the names of their characters.

Word order
Also "their" should be "the"

And Iit's justonly the begeinning of the book !

"just" is OK here, but "only" emphasises the point better
Spelling on beginning