All Right, it seems we have to break this down barney style for you. Once again, octane number is representative of a fuels resistence to detonation. The previous post concerning octane being a hydrocarbon molecule with eight carbons and blah blah blah is true. The purpose of these high octane fuels is generally for racing. In a racing aplication you crank up the ignition advance, boost compression and do lots of other things that would normally destroy an engine without the proper octane fuel.
What is the difference between 89 and 93 octane at the pump? Not much other than a little higher octane and possibly some addative packages, detergents and what not.
Does your car need it? I don't know, if your edecated enough to be able to get on this forum and type something you can probably look it up in your owners manual.