What can you see when diving in Brazil beaches?

Fish. Different kinds. It would vary from place to place. E.g diving in Santa Catarina would be different to say Fernanda de Noronha.....

I'm extremely confused. If you know what diving is like, why are you asking us what you can see? A bizarre post if ever I saw one.

I've never read anywhere that diving in Brazil is "the best". Several countries vie for that honour - the Philippines, Indonesia first among them - but not Brazil, really. Doesn't mean you can't do great diving there though!

I know what diving is.

I say it on TV.

I haven't done it in real life.

I believe the English language skills of the OP may not be that of a native, so let's go easy on him.

Scuba diving, like everything else in Brazil is waaaayy more expensive than in other countries. I suggest you go to google, choose "images" and search "mergulho arraial". It will give you tips of diving in Arraial do Cabo, a small town 2 hs away from Rio where many people go for that.