It heats the water and turns it to steam. The steam drives a steam turbine, which spins a generator to produce power. In some reactors, the steam from the reactor goes through a secondary, intermediate heat exchanger to convert another loop of water to steam, which drives the turbine. Electricity for homes and businesses comes from this generator at the Shearon Harris plant. It produces 870 megawatts.
Pipes carry steam to power the generator at the power plant.
The reactor's pressure vessel is typically housed inside a concrete liner that acts as a radiation shield. That liner is housed within a much larger steel containment vessel. The steel containment vessel is intended to prevent leakage of any radioactive gases or fluids from the plant. Finally, the containment vessel is protected by an outer concrete building that is strong enough to survive such things as crashing jet airliners. The absence of secondary containment structures in Russian nuclear power plants allowed radioactive material to escape in an accident at Chernobyl.