The difference between Presta and Schrader valves.
A Schrader valve is the same type as on your car tire. It uses an actual spring assembly to keep the air in the tube. Big advantage to a Schrader valve is that you can use a gas station pump on every street corner in America to fill it. This is not a substitute for carrying a pump with you, particularly if you have a mountain bike, as there are few gas stations off-road!

A Presta valve is thinner and has a threaded exterior with a small nut on the end. To let air in or out this nut must be unscrewed (not completely only a few turns) .  To seal the air in the nut must be tightened (use your hands only! Tools will cause damage). This type of valve will not work with at a standard gas station pump. You will need to use a Bicycle Specific Pump . If you wish to use a standard gas station pump you will need to get a Presta Valve Adapter .