Karma basically shows you and other users your points. They are earned from helping around the site, assisting other members and over all good behavior. Do not ask for them as they will be denied. They may be given at anytime by a guide/moderator that feels it fit.
You can also earn negitive karma. This is given because you might not have been following the rules, causing trouble, trolling, spamming...etc. You do not want any negitive karma.
So make sure you read over the rules too.