How does mac .dmg files work. ?

A DMG file is essentially just an image, like an ISO in Windows. Now, I can't say ALL OSX programs are installed like this, but for the most part, you mount (double click) the .dmg file, and it should show a new disc on your desktop. In it, is the application. A basic app in OSX is a single file, with all the needed material rapped inside it. All you have to do is drag it to your Applications folder in the explorer-style window (should be on the left hand side of the box). From here you could just leave it in that folder, or you could drag it to your desktop or your dock for easy use. To uninstall, just drag the application to the trash. No sweat.