I recently started playing around with the raspberry pi 2.

I followed the guide on lifehacker to get this set up.

http://lifehacker.com/how-to-turn-your-raspberry-pi-into-a-retro-game-console-498561192

The setup is really easy to get going but I did find a couple of commands very helpful.
updating

rpi-update will update the raspberry pi firmware

Retropi is based on Debian so apt-get is your tool for general updating.
Getting a console

when you are in the games menu hitting f4 on a connected keyboard will open up the console.