The diagram below illustrate how a hydroelectric power station produced electricity. Overall, water from river stored into the dam, then dam use its high level to flow water through turbines at high speed, generators connected with turbines generate electricity.
First of all in a hydroelectric dam, the source of water in dam is from a river. Water is reserved in the dam reservoir known as High-level reservoir because of its height. Beneath the dam, there are gates that open the flow of water in day time and close it in night. When gates are open in day, water flow from dam into the turbines that are at low level at high speed. This high speed of water produce because of height difference between dam and turbine make turbine wings to revolve at high speed.
At high spin of turbines, it run the generator connected to it. And this generator in the end generate electricity. that electricity move from power line into national grid to distribute. Extra water that already passes through turbines dumped into Low-level reservoir.