For this little potato cannon all you will need to do is take any igniter from any BBQ lighter, then insert the two wires of the igniter through the two holes on the side of the cannon. Next wrap a tape of your choice around the igniter to secure it in place. Now that it is in place push the button to make sure there is spark (if not, try moving the ends of the wires closer or further away from each other until you get a spark.) To ensure that the seal around the threads are tight, tightly wrap some tape around the threads. To fire the cannon: put anything that fits snug but not too tight. Now all you have to do is spray some hair spray of your choice in the back, (the cheap stuff works great) then quickly screw the cap back on, now just aim and click the igniter to watch your projectile fly across the room.

here is a video of it shooting