what did they use to fire them in Ancient China? I know that they used gunpowder inside fireworks

Hennie, they firstly input gun powder into the cannon and the put the ball inside. The ball can be made of iron with gunpowder and other ingredients. Then there is a fuse to connect the gunpowder. Once the soldiers ignite the fuse, the gunpowder will explode. As a result, the ball flies out of the cannon. Once the ball reaches the battlefield, it explodes to cause casualties.