Instructions
Insert your Nintendo 64 game into the game slot on your Gameshark device.
Insert your Gameshark device into the game slot on your N64 and turn the console on.
Select the "Select Cheat Codes" option in the Gameshark main menu. Select the game with wish to add the code to in the main menu.
Select the "New Code" option in the next menu. You will be asked to enter a description for your code using the on-screen keyboard. Since you are creating a code, it is preferable to enter "Test Code" as the code description. When finished, press the "B" button, then select the "Done" option.
Enter your code in the next screen using the on-screen keyboard. When creating a code, the best advice is to manipulate an already-existing code. For example, if you have a code that gives you infinite lives, you may be able to manipulate the code to give yourself infinite energy. When finished, press the "B" button, then select the "Done" option.