I noticed that a few people didn't really know what reputation was and didn't really feel like this was a "news/announcements" type of thing. I just came to enlighten you! ^_^
Reputation is individual to each account. It is in the information under the person's profile picture. There is negative and positive reputation. I honestly have not seen negative used very often because everyone on this site is so nice. To the right of every post, there is a little line(or bar((either red or green or both)) with a plus and minus sign.
Clicking the plus sign will give that person one positive reputation!! That is only for if you agree or like their post. Please do not go willy-nilly Plus oneing everyone's posts.
Negative reputation is just the opposite. It gives them minus one reputation DX. If you dislike someone's post or disagree you would click this. The vote/bar is completely anonymous but the person will see the good to bad reputation ratio.
Most every day posts will not have any reputation at all and that is completely fine. Now go my children, fly with your newfound knowledge. I must warn you to use it carefully. Don't overuse your powers of awesomeness. Serenity is out ;D