The difference between a power station and substation is the power station is the place where the electricity is generated using massive electric generators.
Generating electricity can be done through use of natural gas, coal, Nuclear power and even hydro power which is water.
The generator generates electricity from a magnet and copper wire which is sorta like a reverse electric motor and instead of turning from electricity the spinning of the generator creates electricity.
The electricity then leaves the power station at very high voltages and then goes to a step up transformer out near the power station.
Then it gets stepped up even higher using more transformers and then gets to a large substation where transformers step it up or down again to distribute the power to homes, businesses etc.
Near towns there will be a substation that lowers the voltage some and then the power goes either into the ground or up on poles through wires to another transformer that then steps the voltage back down to the 240 Volts that most homes and small businesses use.
The substation is a high-voltage electric system facility and is used to switch generators, equipment, and circuits or lines in and out of a system.
The electric substation also is used to change AC voltages from one level to another, and/or change alternating current to direct current or direct current to alternating current.