To enter, all you have to do is put a map together for the tower defense RPG (here's a guide.) Submit your map to Trendy by June 21, and if it wins both a public vote and a judges' vote you can walk away with $1000, and even get your map included in the game.
The full rules and requirements are over on Trendy's forums. Those of us without any design skills at all will just sit here quietly waiting to see what you put together. Don't mind us.