To use an Action Replay cheat for Pokémon, you will need to first obtain the code for the cheat you wish to use. These codes can be found online or in gaming magazines. Once you have the code, you can enter it into the Action Replay device and activate it.
The way these codes work is by modifying the game's code directly. When the code is entered into the Action Replay device, it will look for the relevant section of the game's code and change it to match the code that was entered. This can have various effects on the game, depending on the code that was used.
It's important to note that using Action Replay cheats can sometimes have negative consequences, such as corrupting save files or causing the game to crash. It is always best to use caution when using these cheats and to make sure you have a backup of your save file before using them.