Hit the spacebar or click (though it doesn't seem to like it) the start button to start the game. Click (though it doesn't seem to like it) on the class you want (red=player 1, blue=player 2) or hit the number key (1 for the wizard, 2 for the swordsman, 3 for the archer). If you choose the wizard then each spell cost spell energy (lightning cost 1, fireball cost 10, and ice blast cost 2). To cast a spell the player hits the key for the certain spell (Player 1: 1 for lightning, 2 for fireball, 3 for ice blast) (Player 2: b for lightning, n for fireball, m for ice blast) If you choose anything but the wizard then you attack with key 1 (for player 1) or b (for player 2). Player 1 moves with wasd, while player 2 moves with the arrow keys.
I did everything, but I grabbed a few of the costumes and all of the backgrounds from google.