The reputation you have is given by other users, if you have been helpful.
The higher your reputation, the higher your points if you give someone rep points. Eg if you have a rep high rep points (1000 for example ), and you give someone rep, it will give then more rep points than if someone with a low rep points gave them rep (10 for example which you start with)
And if you're a nobber you will get negative rep points. Only person I can remember with that just now is some dude from oz.