Plenty of colored balls stick to this wheel. You can fire balls of the same color at them: if you make a group of at least 3 identical balls, they explode. Once you've deleted all the colored balls, you move on to the next level. Keep the balls inside the circle, otherwise you lose! Now and then bonuses appear, like bombs or an 'all colors' ball: use them, because they help you pass to a next level more easily.
Use the mouse to aim and to shoot.