The battery supplies the power necessary to start the engine when the ignition switch is is turned on.

Sensors provide the data necessary for the vehicle's computer to make decisions and monitor everything from simple vehicle information like tire pressure to complexities like the chemical content of an engine's exhaust.

Spark plugs receive current from the distributor and use it to spark combustion in the combustion chamber of a cylinder.

The steering linkage is a system of pivots and connecting parts between the steering gear and the control arms. The steering linkage transfers the motion of the steering gear output shaft to the steering arms that turn the wheels.

The transmission provides the appropriate power to vehicle wheels to maintain a given speed. The engine and the transmission have to be disconnected to shift gears and a manual transmission requires the driver to manually manage this disconnection (using a clutch) and to manually shift gears. An automatic transmission is essentially an automatic gear shifter and handles this process without driver input.