You see that little blue box under your user title?
That's your reputation box.
You start out (I think) with 10 points. It'll say distinguished road, then when you get 25 it'll say something else, and then when you get 50, 75 etc.
When you get 100 Rep Points you get another box, that's why some members have 2, or more.
Now, some members Rep Box's are red. Thats because you can also give bad rep.
The little Green Box you see at the top of your post, when you click it it'll ask you to give rep, agree or disagree, agree being good rep and disagree being bad rep.
Now, if you disagree with someone's post when you're having a discussion you don't give them bad rep, you give them bad rep for spamming or something like that.
You give good rep when you like someone's post, or they're helping someone out.
Yeah. :)