Instructions
Navigate to your "Call of Duty World at War" directory. The directory can be in a variety of places, depending on where you installed the game's files. But this directory is located in the "Activision" folder of your "Program Files" folder, by default.
Right-click the file "common.ff." A list of options will expand, as if you were to right-click a file on the desktop.
Hover over "Open with..." and click "Notepad." The file's contents will open in a Notepad document.
Add lines of code or change the existing ones to customize the game's files. Typically, changing "1" to a "0" will activate the cheat code the number is beside.
Save and close the file to keep any changes you made. These changes will load the next time you start the game.