The Global Positioning System (GPS) works through a constant communication between the GPS device on the surface and multiple satellites in orbit. The way it works is that the GPS device sends out signals and the satellite sends out signals back to it. The data is then analyzed and by determining how quickly the signal is returned by any particular satellite, the GPS device can establish where it is on the surface of the Earth fairly quickly.
This enables joggers to figure out how far or fast they have run, drivers to establish the correct routes to their destinations and even enables companies to keep track of their shipments and vehicles.
One of the nicest things about our world today is the video we can see to help us visually teach our students. Here is a nice video that explains the basics a bit better than we can.