The battery where it all begins
The battery is able to convert stored chemical energy into electrical energy. It is made up of six individual cells connected together in series. Each cell provides 2.1 volts. The battery is considered fully charged at 12.75 volts. A battery stores the electrical energy for the car when it isn't running.
The alternator the workhorse of the electrical system
When the engine is running the alternator will provide electricity for the car electrical system. It will also charge the battery. The faster the engine speed the larger the amount of electricity the alternator will provide. The most common sign of an alternator failure is the battery light coming on when the car is running. An alternator will normally be rated to put out 90 amps of current which is around 1000 watts of energy. The voltage at the battery in a normal system with the alternator charging would be 13.5 to 14.5 volts.
The Starter bringing the engine to life
When you turn the key an electrical signal goes through a wire from the ignition switch down to the starter solenoid. The starter solenoid pushes the bendix gear in towards the flywheel and connects the starter motor to the battery. The electricity from the battery turns the starter which then turns the engine over. It takes about 200 amps of electricity or 2500 watts to turn the engine over. The first starter installed on a production model car was Cadillac in 1912, before that the most common way to start the car was with a hand crank.