Sorry, I still don't get this. What does this module do, exactly?
In short, it 'projects' a virtual resolution onto your actual resolution screen.
It means that you can write your game telling it to use a 1024x768 display -- but by setting the projection matrix, you can project this onto an 640x480 or 800x600 or other size screen as well, without the need to rewrite any of your code. It automatically rescales everything to use that resolution.
Much easier than having your drawing routines and scaling calculate everything individually for each resolution. As far as your game logic is concerned, it always runs at 1024x768, when in reality it isn't.