How do bottle rockets work?

A bottle rocket is like a firecracker on a stick. The bottle rocket is placed at an angle in a soda bottle that is firmly on the ground. Then the bottle rocket's fuse is lit. When the fuse burns down there is an abrupt explosion in the bottom of the rocket that forces it to fly up. When it burns all the way up the bottle rocket, gun powder in the tip of the rocket explodes in the air.