Could anyone explain to me what a cyber sex is?

Well, it comes in different forms.

You can cyber with text, for one, anywhere from forums to email. I used to frequent a roleplaying site and after a while it was infiltrated by a bunch of users who did nothing but have cyber sex in the threads. It basically is just sex that is written. One person writes a portion, then the person (or people, lol) they are cybering with writes the next part... you get the idea.

You can have cyber sex in online games, such as IMVU or Second Life (which gives you.. extensive and colorful ways of doing so). You can also do it via webcam, and so on. In a nutshell it's just some sort of simulation of sex over the internet.

*Agrees with The World Is Ugly*

It's just sex, over the internet pretty much o.O

Either people write what they're doing, over a webcam, or in online games already mentioned.

i could not have said it any better than the world is ugly

Haha! at your age boys know EVERYTHING about sex!