Player 1 uses the WAD keys and S to throw the ball. Player 2 uses the arrow keys and down to throw. Try to score through the opposite goal for 10 points. You can take the ball your opponent by flying through them. Every now and again you may see the snitch. Catch it for 150 points. It ends the game, so don't try to catch it if you are behind by more than 150 points. Watch out for the bludgers, which will go for you if you go too close.
Check out @bigB, because he makes good harry potter games, including this one.