Well when another member makes a post, all their info is displayed on the left of their post (Avatar, posts, stars etc.) And where it says 0/0, right underneath is a Like or Dislike button. If another member likes your post, they press like and your karma gets +1/0 if you are trolling or hating, and somebody dislikes it, you get 0/+1.
When you kissed up in the forum game, I gave you a karma point. Only other members can give you karma, and each member can assign a karma to anyone once per hour.