When the driver turns the ignition key, the current from the battery starts the electric starting motor, which turns the crankshaft in the engine. This crankshaft begins to move the pistons and rods. The fuel pump starts pumping fuel from the tank into the engine. Electric sparks light the fuel, which explodes and starts the engine.

Once the engine starts, the electric starting motor shuts off. Now the engine is producing the power, which has to move from the engine through the power train to the car's wheels. The gears in the transmission start the work of carrying the power to the wheels. There are usually four or five sets of gears in the transmissions of most cars today.

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