Turns out it's quite simple, and you don't need any extra hardware. No taps, no adapters, no kegerator.
- Pull up the lever on top and twist it hard counter-clockwise. The plastic won't break on you, and you do have to twist very hard.
- There's a big (usually red) lever at the base of the keg. Pull the top of the lever down hard. Then take the lever by the hand and pull the entire thing out from the keg. It will travel maybe an inch or so away from the keg, pulling a plastic bar with it.
- You're done! Now just twist the bar at the base of the keg to the left when you want to pour the beer.
The CO2 and everything is built in already, and it's fed into your glass by gravity.
Most people recommend chilling a keg in your refrigerator for 10 hours if it's completely at room temperature. If you just brought it home cold from the store, I'd still recommend letting it sit in there for 2-4 hours, depending on how long it was in your car.
I'm not sure yet how long these kegs last once opened -- I'll be experimenting with that this week.