How can I know who "repped" me, and for what? I started with zero rep and now I have "2"... Is it given automatically for a certain number of posts?
Click User CP to the far top left of page...Once in, scroll down. It will tell you who, if they signed it. If it's a Green box it's good, if red it's bad, and if grey, it's from a newbie with no rep power yet. If you click the thread link in it, will lead you to the post they repped you for.
As Bliss mentioned briefly, you can't tell who repped you unless they signed their comment (or in the comment area). Reps are anonymous unless the person giving the rep points chooses to tell you who they are.