From the mGalaxy configuration options you can set which arcade machines and consoles you want to use and the folder where you keep the respective emulators. For example, if you want to play Super Nintendo and Playstation, you just have to activate them and indicate the directory where you'll find ZSNes and EPSXE (to give just two examples).
From mGalaxy's settings you can also configure any controller you have connected to the computer or keyboard and can even change the frontend's skin by choosing different colors and styles.
Once inside mGalaxy itself, you'll find a perfectly designed interface that makes it easy to start playing. You'll see screenshots for each game you select, a list of your most-played titles, your favorites, etc.
mGalaxy is one of the best options out there to turn your old computer, Raspberry Pi, or any other device that you want into a sort of arcade machine fully capable of emulating and running any video game in the blink of an eye.