Ocarina is a very simple Wii application for your homebrew channel. What it does? Start a game.. but there's a twist of course.
Ocarina checks the GAME ID.. like RZDP01 for Zelda Twilight Princess (PAL). Then it checks the inserted SD card whether it can find a cheat code file for that game: in this case it would have to be name [sd]:\codes\rzdp01.gct .
To create GCT files.. a PC application is bundled in the package. This application is coming with 2 example files. rsbe.txt and rsbp.txt (Smash Brothers NTSC-U and PAL respectively). Using the File menu you can open, them and select the cheats you want.
Note that unlike an Action Replay you can modify codes with XXXXXXXX inside them.. it will always ask you to store modifications to its application memory I added this question so that people do not cry if a code is messed up - the actual cheat code file will not be modified until you save it in the app.
Once you're done selecting codes: click on "Export to GCT"... and the rest should be pretty straight forward! Insert your SD card.