Up here, the main black/white supply lines typically pass through the "light outlet" (the ceiling box where the light and/or fan are mounted), and continue along to other outlets on the same circuit. A switch is wired in by running a wire pair (black+white, or black+red) from the ceiling outlet to the switch. When the switch is "on", the current just loops into the switch on one wire, and then back to the fixture (fan, light) on the other wire.

That's how it works here except in residential what you will see a lot is a 3wire (black, red, white, ground) run from the switch to the ceiling box to accomodate a ceiling fan as well as a light kit on the fan. That way you would tie the black to the white at the ceiling box (making the whit hot) then pigtail off the white in the switchbox to two switches (one for the fan and one for the light) then you would hit the fan with the black and the light kit with the red (or vise versa).