Wacom Airbrush pen for Intuos3 - How to use?

I recently bought a Wacom Intuos3 Special Edition A4, which came with an extra pen, namely the Airbrush one.

I may be the dumbest person ever, asking about this, but I can’t seem to find any resources out there, as for how it’s supposed to be used: examples, tutorials, manual, anything.

How do you use it?

Reason for my question is, that there is a finger-wheel on it, that I can’t find any settings for, in the Wacom Tablet manager software. (Note: I’m on Mac, so I’d be happy for any specifics regaring that platform.) Most often, it really doesn’t do anything when I flip that finger-wheel… :-(