It can be used for water supply , hydroelectric power (electric power), control floods and for irrigation .
Electricity - hydroelectric power occurs when the water passes through the dam. The electricity is made by a turbine , made of coils surrounded by magnets and the magnets spin over the coils to produce electricity.
Control floods - dams catch the remaining water so it doesn’t run off downstream. And dam operators can let the water go out when it’s needed
Irrigation- the waters stored in the damm can be used for irrigation so that the farmers can use water for growing their crops
Hope this helps ☺️