Basically, every month, a bunch of artists, who each join one of two "competing" teams, draw each other's characters. These drawings are called "attacks", and people can rate attacks. The more positive ratings on an attack, the more points that artist's team gets. There's no "negative" rating button, so the overall atmosphere is very positive. It's not REALLY a competition, more a chance to have fun drawing other people's characters!
This is my first year doing it, and It's super enjoyable.