This video explains the working of a starter motor with relevant animations. The starter motor model shown here is a pre-engaged type starter motor. In this type, the pinion engages with the flywheel before the motor starts to spin and hence the name.
The starter motor is powered by the car’s main 12-volt battery. To turn over the engine, the starter motor requires a very high electric current, which means the battery has to have sufficient power. Watch the video from TecknoMechanics for more info:
When DC power from the starting battery is applied to the solenoid, usually through a key-operated switch (the “ignition switch”), the solenoid engages a lever that pushes out the drive pinion on the starter driveshaft and meshes the pinion with the starter ring gear on the flywheel of the engine.
The solenoid also closes high-current contacts for the starter motor, which begins to turn. Once the engine starts, the key-operated switch is opened, a spring in the solenoid assembly pulls the pinion gear away from the ring gear, and the starter motor stops.