The ignition system of an automobile draws electrical current from the battery, increases the voltage using an induction coil, and distributes the current to the spark plugs to ignite the fuel-air mixture. The distributor and an ignition-timing system ensure that current flows to the correct cylinder as fuel enters the system, keeping the engine firing efficiently.
The ignition coil inside the engine functions as a step-up electrical transformer. Inside it are two coils of wire, one connected to the battery and one connected to the spark plugs. As current flows from the battery through the coils, it creates a magnetic field. This field induces a current in the other set of coils. Since the coils on the spark-plug side are much more numerous than those connected to the battery, the voltage increases substantially. This allows the current to jump the gap inside the spark plug and create a spark inside the cylinder.
As the engine works, it draws current from the battery. This charge is replaced by the alternator, which uses the car's motion to drive a spinning magnet inside another set of coils. This generates a current, which flows to the battery to replace the charge spent driving the ignition sequence.