Essentially, it allows you to work on several desktops at once. Your physical screen is considered one out of several virtual screens, and you can switch between these. This effectively multiplies your working area since windows can reside outside your currently visible desktop and still be switched to simply by switching to another desktop.
To configure PageMage, open the "Screen" settings object in your "System setup" folder, or select "Properties" from the PageMage context menu.
For more detailed explanations, select from the list below: