In the simplest terms, a float travels up and down with the waves and operates a pump to pressurise sea water which is piped ashore. Many individual pumps are connected together to produce substantial amounts of pressurised water.
Once ashore the pressurised sea water is used to drive a standard hydroelectric turbine to produce electricity.
This pressurised sea water can also be used for directly producing fresh water by the reverse osmosis desalination process. Both fresh water and electricity can be produced simultaneously