Question

How does geothermal energy work?

Answer 1

Geo gives a hint to "from the earth" and thermal hints towards "heat"
Since deep in ground is normally hotter than the air and the surface the earth, geothermal energy is the capture of heat energy from withing the earth

Answer 2

How does geothermal energy work: Concepts and Ground Temperature At a depth of below four feet, the ground temperature stays a constant 50 to 55 degrees year-round. During the winter, a geothermal system absorbs this extra heat from the earth and transfers it into your home.