It's actually really simple. When you log in you are presented with a list of apps that have "points" assigned to them. Every time you review an app on iTunes that is in this list you gain one of those points for yourself.

You can then take points that you accumulate and assign them to your app. The more points it has, the higher your app appears in the list. when an app runs out of points, it's removed from the list. But if anyone assigns more points to it (either you or your fans) it jumps back up on the list.