I have wanted to see this movie sincefor a long time but I waited.

We say "for a long time" not "since a long time". I removed the period because it should connect with your next thought.

BI have wanted to see this movie for a long time but I waited because I knew this movie could change the way I see the world.

This should all be one sentence. Technically, "because I knew this movie could change the way I see the world" is a sentence fragment. You need a subject and verb. It makes most sense to connect this to the previous sentence.

And it makde me cry, by the way.

The way you had it before was another sentence fragment. Remember, you need a subject and verb for each complete sentence. I added one here by adding "it".

I have always loved Ppoetry, Pphilosophy, stories about wise men, and of course, Robin Williams.

Because it's something that has always been, you'll want to use "have always" instead of just "always". I love Robin Williams too!

For me, itIn my opinion, he was one of the best actor of his generation.

"In my opinion" is a bit more natural than "for me". "It" would be more appropriate for an inanimate object. Here, you would use "he" because you're referring to Robin Williams.

This movie speak aboutcovers topics like: dreams, the sense of life, and the necessity to be a free spirit and always follow our own way.

You could say "the movie speaks about" but it's a bit more natural to say, "The movie covers topics like..." When you are listing things in a sequence, remember to add "and" before the last thing in the sequence.

It was really good.

This is fine but a bit repetitive. You could just choose one of these sentences.

I've wanted to see this movie sincefor a long time, but I waited.

The "because" in the next sentence should be part of this sentence.

Bbecause I knew this movie could change the way I see the world.

*see above comment*

And make me cry, by the waI knew it would make me cry.

In "proper English" you should never start a sentence with "and," but plenty of native English speakers do it (especially in spoken English) that I don't think it makes sense to correct it.

I've always loved Poetry, Philosophy, stories about wise men, and of course, Robin Williams.

For me, ithe was one of the best actor of his generation.

Another common phrase is "To me," as in:
"To me, he was one of the best actor of his generation."

This movie ispeak about dreams, the sense of life, the necessity to be a free spirit, and to always follow our own way.

If you wanted to use the word "speak" you could use the phrase "it speaks to" to get the same point across:
"This movie speaks to the concept of dreams..." (but that feels like a really "fancy" way to speak, and would generally not be used in normal speech).

Fortunately, I didn't watch this movie when I was a teenager, because I was already was a rebel.