The distributor is part of the ignition system, that creates, and distributes the spark to the correct spark plug, at the correct time in the firing sequence.The distributor is the heart of the ignition system. Its three basic functions are to trigger the firing of the ignition coil, to control timing advance, and to route or distribute the coil's high voltage output to the individual spark plugs.
If you go to the following site, there is a cool description. Click on the links to see what the other parts do, and their relationship to each other.
A distributor distributes spark at the correct time. If it is malfunctioning, it can cause your engine to run rough and will also affect the efficiency of the engine (thus, lower miles per gallon of gas).
〉 Answered on May 15th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management