Reputation is just a way to know how good and honest a user is. Users throughout this forum can "Rep Up" each other. If you want to rate someone, click on the green or red button under the member's avatar who you wish to rep. You can give a positive or negative (green = positive, red = negative). You can give each user one reputation, however you can give them additional points but you need to wait for 3 hours to do so. Once you click on the green or red button, you will be redirected to a page where you must enter a comment. Your comment can be viewed by any member. Once your comment is submitted, you will be taken back to the topic that you were viewing. Once you have 5 posts, you will be given the ability to rep users. Please DO NOT abuse the reputation system. This includes giving a negative reputation to someone for the sole reason that they gave you one, and spamming positive or negative reputation.
You may view the reputation of a user on every post that they make, by looking at the left side of each post under the members' avatar. The respective reputations can also be viewed on the profiles.
To view who has given who reputation, go to the users profile and click "Who changed my karma" located beneath the users avatar. You can also view who that user has given reputation to by clicking "Whos karma have I changed" located below the previous option.