Instructions
Press the eject button at the top of the GameCube and insert the GCN Action Replay disc. Turn the console on to automatically launch the disc.
Enter your country by scrolling through the list of options, using the GameCube controller's analog stick. Press "A" to choose the country.
Select the game you wish to enable cheats on from the "Game Select" menu. Press "A" when the game is selected. Press "B" to return to the previous screen.
Hover over the wanted cheat and press "A" to select it or highlight the "Add New Code" option and press "A" to enter a new cheat code. There is no limit on the number of cheats that can be used on one game. Press "Start" on the GameCube controller to complete the cheats.
Remove the Action Replay disc when prompted by the GameCube. Insert the game for which you've just entered cheats.
Close the GameCube to begin the game. The cheats will automatically be included.