How a hydroelectric power plant works, including why dams are built as parts of large hydro power plants

Hydropower plants they do capture the energy of the falling water which generates electricity.

 Turbines convert kinetic energy which is of falling water into mechanical energy. The generator will then convert mechanical energy.

The generator will then convert mechanical energy which is from the turbine to electrical energy. Dams are being built to increase potential energy for it to fall from a higher distance.
The greater the potential energy which is above the surface of the earth the higher the substance which is being suspended.