What is the role of automotive starter solenoid switch is? Composed of those parts?

Automotive starter solenoid switch attracted by the coil (copper thicker), holding coil (thicker copper), iron, copper contacts, the return spring. Its role is to make the core through the coil is energized to move the starter clutch gear sent to the engine flywheel ring gear, when the clutch and flywheel ring gear coupled to the power supply through contact copper turned starter, the starter rotation, start the engine .