Hydropower uses high-pressure water to turn the electric generator. Water at a higher elevation, either at a naturally higher elevation or raised by a dam, is put into a pipe called a penstock, where it travels downhill. As the water falls it moves faster and gains pressure.
When it arrives at the powerplant, this high-pressure stream of water shoots at a water wheel called a turbine, making it spin rapidly.
The turbine is connected by a shaft to the rotor of the electric generator. The rotor is really a wheel with large magnets on it. The generator rotor spins inside a large coil of wire called the generator stator. Spinning magnets inside a coil of wire causes electric current to flow.
The electric power from the generator goes through a transformer where the voltage is increased before it is put on the transmission line to be brought to town.