Spring is required for shooting. Make sure that the spring is big enough so that the rod on the cannon ball can fit through, but make sure it isn't too big that it can't fit through the chamber. Gluing the spring inside the chamber isn't required as long as you aren't worried with the spring flying out each time you fire it. For the wheels, put the Wheel with Stick through the hole on the outside of the Barrel, then slide the Wheel with Hole at the end of the stick (this part shouldn't require any glue, but it's optional)