Chassis: Holds different parts of a car together.
Engine: Where chemical reaction between fuel (gas) and air results in power generation.
Gear System: Transfers the power from the engine to the wheels.
Wheels: rotatate on the road and move the car along.
Steering System: Allows the driver to direct the car to the direction he/she wants it to go.
Suspension System: Springs
and Dampers (shock absorbers) give a smooth ride when you pass over
puddles or bumps on the road.
Body: Hides away the internal parts and also isolates the passengers from outside environment.
Brake System: Allows the driver to slow down or stop the car.
Electrical System: Battery, generator, wires, lights, ....
If you want to learn more about cars, check out this site:
http://auto.howstuffworks.com
You can find very nice and dynamic simulations of car parts and sub-systems.