What makes a Zeppelin go?

Answer 1

The gas inside the shell of the airship (a helium mixture these days, though hydrogen was widely used until the time of the Hindenburg disaster) is lighter than the nitrogen and oxygen that makes up the bulk of the atmosphere.

The helium seeks to rise to the top of the atmosphere (and beyond, into outer space), but is contained - and partly weighed down - by the shell of the airship. Through a careful balancing of the helium mixture and the weight of the craft and its cargo, it can be made to float at a given altitude.

Once airborne, giant steering fans attached to the gondola (the cabin beneath the airship's shell) provide both propulsion and the ability to turn. When the ship is ready to land, the pilot vents helium, making the airship less buoyant and returning it to earth.