Install Wii homebrew if you haven’t already.
Install the homebrew application GeckoOS, which can launch a game with cheat codes enabled. (This function used to be performed with the Occarina application, but its functionality has been folded into GeckoOS.)
Choose a method for creating the GCT cheat files that GeckoOS needs. There are three choices:
Accio Hacks is a Wii homebrew application that allows you to download and manage cheats directly from your Wii. It has some limitations (it is still in beta) and sometimes fails to connect to the Gecko cheats database, but when it works it is the simplest approach.
Online GCT Creator can be accessed from the Gecko Codes website. It is more flexible than Accio Hacks but requires you to manually copy your cheat file to your SD card.
Gecko Cheat Code Manager is a PC application that lets you work with text files downloaded from the Gecko Codes website. It is the most flexible and powerful of the Wii cheat code managers but it is also the least convenient to use.