The cannon is a simple and sturdy assembly (image 1).

The tab, protruding out of the assembly at the bottom of the picture, pulls the launch pad back until it latches into place (image 2). The launch spring is now loaded and the cannon ready to fire.

The latch tab (long slender groove on top of the assembly) can then be pushed to fire the cannon. Typically this is accomplished by pulling the trigger, but her it is shown with a pen tip (image 3).