You're referring to the GameShark device for the PlayStation 1, specifically version 6. The GameShark was a popular cheating device that allowed players to enter cheat codes to unlock various benefits in their games, such as infinite health, ammo, or unlock all levels.
This device is "Plug and Play."
Users could add their own codes found in magazines or online using the on-screen keyboard. How to Use GameShark PS1 Version 6 gameshark ps1 version 6