people can add too you rrep by clicking the little balance thing and making a comment if you help them with something or you have a nice game shot in the game shot gallery for instance.
Well, if you are kind to someone and/or help them they may choose to award you a reputation point. You can also award others 'rep' points by clicking on the scales underneath their avatar. I'll give you some now for example...
EDIT: Sorry hascet, I think we posted at the same time.