can someone tell me what is an exploit and how to use it ?
does someone know where I can find infos or txt about it ?

i think you got somethings confused. exploits are not an "it".

All people mean when they talk about exploits is just making use of a security hole in software or hardware.

Just like politicians exploit the public, same deal. It means the same thing...

Now onto your question

[quote]
can someone tell me what is an exploit and how to use it ?
does someone know where I can find infos or txt about it ?
[/quote]

You can find out about all the latest major exploits by signing up to the BUGTRAQ mailing list:

http://www.securityfocus.com/archive/1

Judging by your question I would venture to say that you should probably not be using any well known exploits just yet.

As with all hacking, dont do it unless you understand what you are doing.

but don't get into the trap of using expliots the whole time and becoming a script kiddie. try and find stuff out for yourself as well.

useful *nix scripts are called exploits, too.