Reputation is a way of praising someone for contributing to a community atmosphere and posting worthwhile posts and content.
Underneath each persons name when they post is a little icon that looks like scales . By clicking that you can give a user reputation points for that particular post. But there's some rules. You can't just go blindly handing out reputation unless you really think they deserve it. The term for giving reputation is called "repping" or "giving rep". Try it, I'm sure someones made a good post today and deserves credit!
This website has customized settings for reputation power, here's the basics.
Default reputation: all users start at 0
Register Date Factor: for every 360 days, user gains one point of rep factor
Post Count Factor: for every 1000 posts, user gains one point of rep factor
Rep Point Factor: for every 100 points of rep, user gains one point of rep factor
Min Post Count: user must have 30 posts before rep hits count on others
Min Rep Count: user must have 10 points of rep before rep hits count on others
Daily Rep Count: users can rep 10 times a day
Rep User Spread: you must rep 10 different users before repping the same user again