Instructions
Open Project 64 and go to "Settings," then "Options," then uncheck "Hide Advanced Options."
Highlight and copy a Gameshark code from a website. As an example, for "Legend of Zelda: The Ocarina of Time," there is this Gameshark code: "8011B9E3 0020 Beta Quest." The first two sets of characters denotes the code itself, and the rest is a code description. The formatting of the sets is important.
Open the "Legend of Zelda: The Ocarina of Time" game ROM, then press "CTRL-C" or go to "System" then "Cheats." Right click on this menu and select "Add New." Name the code in the top box, and paste the character set in the code box to ensure the formatting is correct. Click "OK," then check the box next to the new code to activate it.