Right now, you probably have a negative reputation, and my understanding is that the system is kind of borked. IIRC, downvoting decreases reputation, upvoting does nothing, and boosting (akin to a Twitter retweet) increases reputation. From other comments, I believe that this is likely to change before too long.
If, like me, you saw a negative reputation after you got on and started to worry that you were doing something wrong, I wouldn't worry.