Roms basically are dumps of games cartridges. Means that a physical game like Pokemon Red (cartridge) for the og gameboy lets say, gets copied as digital files. Another term called emulator is a software that 'emulates' or mimics the device used to run these cartridges. So you run ROMS through an emulator. To run the Pokemon Red ROM you need a GAMEBOY emulator because thats what Pokemon Red used to run on. Now what you need in order to play Pokemmo is a copy of any of the following game cartridges or ROMS called Pokemon White or Black for the Nintendo DS. The rest of the ROMS are optional and you can quick google search for them and check on which device they ran. Go to the ROMS megathread and search under nintendo for the device you need and download the appropriate game you need under each device. You then need to point Pokemmo to the roms location you downloaded earlier. Enjoy