It's pretty basic. See the plus and minus signs on the right of this post? They can give or subtract reputation. Click the plus sign if you like someone's post. This will make their reputation go up by 1. If you dislike, or are bothered by a post, you can press the minus button. Their reputation will go down by 1. For example, your topic now has a green bar next to it because I pressed the plus sign. It would be red if I pressed the minus. And now, if you look to the left, your reputation is 1. In addition, you can't change a plus to minus, or vice-versa, and reputation can go into the negatives. Hope this helped :)