The guns were what are called "matchlock" muskets.

Powder and shot were put in the end of the barrel and rammed down to the bottom.

Some powder was put in a little pan on the side of the gun. You can see it in the picture, it has a cover that swivels over it to keep the powder dry and stop it falling out.

The head of the dragon was pulled back and a piece of burning match put between its jaws.

musket

Matchlock Musket

When the trigger was pulled, the head shot forward, setting fire to the powder in the pan.* The flame went through a little hole and set fire to the powder in the barrel - BANG!

* This is were the term "a flash in the pan" came from!