Okay, I'm going to keep this as simple as possible
Realm of the mad god, created by Wild_Shadow is a game with 13 classes (which you unlock by leveling up) With a max level of 20, you go around leveling up, killing monsters and oryx's minions, and when you kill all his minions (this may take 1-10 hours depending on how many people are playing, what level they are etc.) you are teleported to oryx's castle where you kill more of his castle minions and then eventually oryx. Once you defeat oryx, the server restarts and every one will be rewarded a drop. If you die, you start at level one.
Yeah, it's a great game you can post anything realm of the mad god related below play it here:
http://www.kongregate.com/games/Wild_Shadow/realm-of-the-mad-god