Reputation shows how good of a user you are according to other users. Each person can give you one rep point per post. If you have 0 you are either not very known or no one cares enough to drop you a rep point.
If your post is laughable people will also drop you some rep. This is common on the spourm where its called karma. Its the same concept really.
A good word of advice, don't take it too seriously. I have seen people get rather carried away when it really does not matter.