What do the power button and Overdrive Off do?

So What exactly does the power button do? Does it increase power, or just waste gas? What does driving with overdrive off do exactly do? Does it work with differnet gears or what?? Just the how/where/why of these two things, please.

The power / normal switch changes the shift points of the auto transmission. It's seen in many trucks as a "towing" button or switch. Helps when you're hauling a load uphill, it'll rev up a little higher before shifting to keep power to the wheels under load. If you're driving on flat and not hauling a trailer, you won't see much more power and probably will see a mileage drop.

The overdrive off button simple disables the top gear of the auto transmission. Basically turning the transmission into a 3 speed auto instead of a 4 speed overdrive auto. Not much use for anything I've come across, except maybe when I want to pretend I'm driving standard and I jab the button right before I pull out to pass someone on the highway and push it again once I pull in ahead of him.