The geothermal power plants use the heat of the deep of our planet (it increases as you go down towards its center).
Through the fractures of the rock layers, the water vapor rises to the surface and is intercepted by geothermal wells.
The steam supplied from the wells is then conveyed in pipes and sent to the turbine where the energy is transformed into mechanical energy of rotation.
The turbine is connected to the rotor which, rotating, transforms the mechanical energy into electrical energy that is transmitted to the transformer.
The transformers are used to step-up the voltage and for the auxiliary systems of the plant.