[ales]

It does exactly what its name implies - it distributes. What it distributes is the high voltage impulse from the coil to each sparkplug at the exact time when the spak is needed in this or taht cylinder. In contact type ignition systems it also sends a signal to the coil when to generate that pulse and then distributes it. In newer, contactless ignition systems the distributor just distributes the pulse, whlie the time of its generating is controlled electronically (with the help of a hall sensor or a crank angle sensor), and the latter is more functional as it can incoporate more ignition-related features, like knock sensors, which can save your engine in case of detonation by retarding ignition timing, but that's already a whole different story.

Here is a rather good drawing of the distributor. See if you can see how it works



Alex