What does the valves in the cars mean?

there are valve stems on your tires where your fill them with air maybe that's what you are referring to. there are also EGR and PCV valves there are also valves inside your engine try the link below to explain better the valves basically let air in and out of the cylinders you have an intake and exhaust valve for each cylinder

http://en.wikipedia.org/wiki/Image:4-Stroke-Engine.gif