Retroarch is actually more of a modular emulator interface than a frontend which allows you to plug emulators into it by way of 'cores'. It enables you to run classic games on a wide range of computers and consoles through its slick graphical interface. Settings are also unified so configuration is done once and you're all set for every emulator. 

We show our recommended settings for the X-Arcade in Mode 1 below, but if you are starting from scratch you can simply download our retroarch.cfg file and drop it in your RetroArch directory (overwriting the original). When you run it the first time it will fill in the rest. If you have an existing setup note that this will overwrite your settings. 

RetroArch Support:

RetroArch Official Setup Documentation

RetroArch Official Forum

Reddit /r/RetroArch