Your goal is to shoot the white ghosts. Each white ghost is 1 point but if you shot a brown ghost, you will lose a point. Also you lose the game if the white ghosts gets to close to the knight. Press the arrow keys to move in the corresponding direction. If you move to far up or down your character and the wand which with you shoot will become distorted. So do not go to far. Also to shoot the ball, simply press the space bar as said in the tutorial if you choose to use it.
Go check out dabdaniel1234, he is the one that created the original game and is also my other more serious account despite the name.