The only thing you need to use the app is to install the correct version for the corresponding iOS device. Once you've done that you will need to associate it with your computer, which only takes about a minute, and then you'll be ready to go.
By default, that new monitor will be set as placed on the left of the main monitor, by this way, our new monitor will be an extra piece of desktop where we can work as usual. We'll be able to drag windows there, and work as if it was a common monitor... with no messy wires around.
Furthermore, as you are now using an iPod or iPad, you'll be able to use the mouse as usual or take advantage of the touch screen and use your fingers to draw and interact.
Use your new monitor to play youtube videos, play flash games and, in short, use it at your convenience, because now you'll have a new and wonderful screen you can move easily to show something to your partner or just to have those chat windows and extra stuff while you work.
Air Display is a really interesting application that offers you that extra desktop space you needed.