As of October 2015, Nuclear Power makes up ~ 21% of the baseload generating capacity of the UK National Grid. Link to Gridwatch ( Real Time Usage )
All of this generating capacity is based upon Fission. This is because, at present, Fusion cannot be used to generate electricity commercially.
The above diagram shows the basic sections of a modern Fission Power Station.
This power station works exactly the same way as any other thermal power station, by heating water to make steam, which drives a turbine and generator.
The only difference is that the water cannot be heated directly, without the water itself becoming radioactive, so a heat exchanger must be used.
The video below shows a explanation of the function of each part of a Nuclear power station.
The core of a Nuclear reactor has several different parts, all of which must work together perfectly in order to prevent a serious Nuclear accident:-
Fusion Power Stations
Fusion power stations are currently in development, but at present, there is no commercially viable Fusion reactor.
This is because, in order to cause Nuclear fusion to occur, we must recreate the temperature and pressure only found in the heart of a star.
The video below shows the basic design and function of a prototype Fusion reactor.