A gearbox is the gear arrangement in the drive train that provides torque and speed conversions from the engine to the wheels.
A gas tank is a storage container for fuel found on any automobile.
The gas gauge (fuel gauge) shows the gas levels in the vehicle. When the gas tank begins to empty the gauge will reflect this and when it gets close to empty a “low fuel” light or something similar should appear on the instrument panel. The main indicators on a gas gauge are “F” for “full” and “E” for “Empty” as seen below. It is always a good idea to use this gauge as a “guest-a-mate” of how much fuel is in the vehicle.