Just plug the micro-SD card into your Raspberry Pi 4 (4/8 GB) (others might work but were not tested) and start playing!

NOTE: First boot will take a bit longer.  Once booted, it will load the interface.

Guides and Manuals:

Over-scan (fix black bars) - https://youtu.be/DeJCUQZB8b4

PS4/PS3 Controller Bluetooth Setup - https://www.youtube.com/watch?v=HddVZqno9Zs Xbox 360 Setup -  https://www.youtube.com/watch?v=-52SfcluhKA

Full RetroPie Documentation - https://retropie.org.uk/docs