How does a dc generator work?

By using a gas engine to drive a dc motor. Motors are cool in the way that if you give them power they will spin and if you spin them they will make power. There is a ball of coiled wire in a motor and when it spins the magnets in it try to resist the spinning but if it succeeds in spinning then electrons will be pushed through the coils by the resistance of the magnets and ultimately through your electrical appliance's.