What is the purpose of geothermal energy?
To generate electricity.
Geothermal electricity, is generated from water heated from geothermal activity rising and moving a turbine than powers a generator.
This hot water is then either recycled, which is done by cooling it and then putting it back into the pipes that lead into the ground, Or it is used in local houses to heat them.
Geothermal energy is widely used in areas of geothermal activity, such as Iceland, where it is a renewable source of power and has almost no carbon footprint (the only bit being the construction of it).
There is also a lot of research in this way of generating electricity, so it is becoming more efficient and cheaper to set up all the time.
The only disadvantages of it is that it can be costly to set up, the geothermal activity can reduce or disappear, dangerous substances can surface and it has a small chance of triggering earthquakes.