When you take apart an electircal outlet, you'll see a bunch (and I mean a big bunch!) of little windmills that are providing the needed electricity for the outlet. When a plug is inserted, several little "Outlet Gnomes" then hook up the prongs to the windmills and voila! there you have your power!
That's the way I see it, although I could be wrong.
Nonetheless, is this really an honest way to research your homework?