The Game Genie is a "game enhancement" device made by Galoob and Codemasters for the NES, Super Nintendo, Game Boy, and the Sega Genesis game systems. You plug a game cartridge to the Game Genie, and then the whole thing to the respective game system. Afterwards, you'll see a screen that lets you type in a few codes (be it from the Game Genie manual, GG codebooks from subscription, or anywhere else). Finally, you can play a video game with those special effects that you have typed in (or make things harder!).