Little button on the bottom left of all posts. Below the name, country and online status. It says 'karma'. You can click that when you read a post that you feel strongly about - maybe they helped you, maybe they made you laugh, maybe it just struck a nerve with you. Green karma (agreeing with a post) is positive, Red karma (disagreeing) is negative. Measured by the green squares next to your post count.
It is a system that is highly abused by many (so-called 'karma whores'). It used to help you tell who was a big contributor - but now it tells you nothing really. Same with post count - there are new members who go over the Chat&Conversation and post hundreds of times in one day - jacks up their post count.
It is against the Terms of Service at Elite to start a karma thread - to start a new thread simply for the purpose of giving out karma.
You can check your karma levels by going to your Profile, I think.
Now I am locking this, so nobody can post a reply to it, so it stays a kosher, informational thread.