[jstraw]

Is this something you put under the tripod head that allows you to level below the head?

No, you still mount your camera on top of the tripod. You can use the leveling base with, or without a tripod head. If you are shooting multi-image panoramas, you will need some way to rotate (pan) the camera. This can be accomplished with a tripod head with a built-in panning function or a panning base (such as the Feisol PB-70 or PB-90).

Based on your full answer, I've decided that the answer to this question is actually "yes," since that's just what I meant!

All I can see is that it has a knurled shaft and a level on the side other than that, it's a mystery to me.

The knurled shaft is actually the handle. You twist the handle to lock/unlock the leveling base. Once unlocked, you use the handle to level the platform using the built-in level as an indicator. Then, you twist the handle to lock it in place.

That vertical shaft is a handle? I assumed that it went down inside the center column based on the screw holes around the platform. If that's the handle then I have no idea how that item is attached to the tripod. Can you clarify?