Rep scores allow you to click on the user's name to see how other users have voted that person's questions and answers as being useful or not. By clicking the up and down arrows on the left side of the questions or answers, you can add to their score for good answers or deduct from it for answers that aren't useful. The following is an explanation provided by Ryan, the site founder:
"EHelp.com is a reputation based community. You can gain reputation scores by asking quality questions (clear and useful) and posting helpful answers. When other users vote your question or answer up, you will receive 5 points of reputation, but when they vote it down, you'll lose 2 points. If your post gets removed by the moderator/reputable users, you'll lose 20 points."