Your job is to hi every monument on your way. Use the arrow keys to rotate and pan the cannon. Press and hold space to load the cannon and release to fire, "c" on keyboard to switch to the fireball camera while it is in the air. Snowmen will explode when hit but can catch a fireball with their hands or they will melt when you hit the monument. There is limited number of fireballs available (bottom right screen) and the shooting angle indicator at the bottom left screen. Wind direction strongly affects the fireballs trajectory, so take it into account. Good Luck!