What it does is that u put it in a D's or dsi and then insert a game to the top part of the action replay. U than start up the system and the action replay will start up and if it has a list of several thousands of games and cheats. If the game u have inserted has cheats it will automatically search for cheats for thatvgane that u can then use. Its like a gameshark if u have ever used one of those. Say u play Pokemon u can use it to get all the items at the beginning of the game. Or u play Zelda u can give yourself infinite life. Etc....