Shoot the nasty rats that are trying to take your cheese >:( Well actually you're a cat so you don't really care for cheese, but you don't enjoy chasing down those suckers either! Shoot 'em I say!
Aim with the mouse Shoot with the Left Mouse Button
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.