Keep clear of all flamable materials, do not use too much fuel and protective eyewear is a must.
Demonstration comes with a homemade cannon, a tennis ball, a lighter and lighter fluid.
To load push the tennis ball into the tube as far as it will go. Add only 10 drops of fuel into the fuel hole at the back of the cannon. Shake vigorously, allow any excess fuel to drain out. Use the lighter to fire the cannon.