There's a place over on the left of every post where you can "rate" a person's post: "I approve" or "I disapprove." If hover over this (I think it might be a symbol of a scales but can't tell for sure), you find out that you have a chance to "add to" the person's reputation.

Well, you also have a chance do subtract from the person's reputation, but that isn't mentioned.

I am sorry to see a rating system creeping back in. I thought it was disposed of quite a while ago....