Stupid questions that don't deserve their own thread thread

Can someone explain how the fuck manual hub lockers work? I've never had a 4x4 until now and I don't understand what they're used for.
Do you leave them unlocked for driving around town and just lock them when you go offroading?
Do they have to be locked for the car to actually transfer power to the front wheels? If that's the case, what's the point of the 2wd/4wd selector if you also need to go out and lock the hubs?
If I put it in 4wd and leave them unlocked, is it 4wd or still 2wd?