Why don't you look for manuals about the type of system/OS you want to "hack". I would recommend learning about Unix, Linux, BSD, Apache, etc. That's a good place to start.
Of course... this is all just suggestion. It depends on what you want to do, in general terms.
Oh yeah... one last thing. Allocate some brainpower to BlackKnight's sig... see if you qualify. Good luck.
Back off, man! I'm a scientist... - Peter VenkMann