How does an airport control tower work?

The control tower does just that - controls what happens on, and above the airfield.

They use radar to see where planes are in the sky and radio to keep in touch with planes and other vehicles. They 'queue' incoming planes ready to land, and marshal planes on the ground so they move around safely.

They have ultimate control of every vehicle on the ground - nothing moves without permission from the tower. That applies whether it's a maintenance vehicle or a Boeing 777 !