Geothermal energy uses heat from the Earth's interior. The inside of the earth is very hot (up to 9,000 degrees Fahrenheit), and that heat moves from the inside of the earth towards the earth's crust (the outside).

Have you ever seen lava coming out of volcanos or hydrothermal hot springs? The lava and the water in these examples have been heated because they were deep inside the earth at one point and then moved towards the surface of the earth.

Hot water or steam from the earth's interior can be used to generate heat or electricity. You can find out more about this by visiting the following site:
Geothermal energy (GEO)