Not a silly question at all.
The function is called Spaces, which lets you switch between different desktops. You can read about Spaces here: Mac 101: Using Spaces to organize your windows and applications (Mac OS X v10.5, 10.6)
If you click the symbol with the two opposite arrows, in the upper right corner of the window of an application that supports it, an app will open in full-screen mode.
Then you can configure the gestures that control Spaces in Applications > System Preferences > Trackpad > more gestures.
On my mac, for example, if I do a three finger swipe upwards, it opens Mission Control. Mission Control organizes the different desktops in Spaces. I can open a new desktop for Spaces, remove a desktop, or switch apps between desktops.
It probably doesn't make much sense when this is described in words, but if I were you I'd just jump in and experiment with it a bit. If you have more questions report back here.
Message was edited by: arthur