If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Shoot off a cannonball with as obvious goal to break the lamp in each level. In later levels, platforms will block your way to the lamp, find a way around them.
Use the Mouse key to aim the cannon and set the power of the shot, the further away the mouse cursor is from the cannon, the more powerful the shot is. Break the lamp.