Yes you need a wii game or gc game, i think it's more easy with gamecube.
First of all you need to install Nintendont. (Don't be worried of the many installation, usb loader gx needs nintendont like a plugin, but you will need only to use one spftware to launch both wii and gc games, even if both of them must be present on the sd card)
Create a folder called Nintendont onto your sd/apps, then put inside it this file https://github.com/FIX94/Nintendont/blob/master/loader/loader.dol after you have renamed it to boot.dol from loader.dol
Also put in the same folders these three files:
https://github.com/FIX94/Nintendont/blob/master/nintendont/icon.png
https://github.com/FIX94/Nintendont/blob/master/nintendont/meta.xml
https://github.com/FIX94/Nintendont/blob/master/nintendont/titles.txt
Then go to usb loader gx,press on the settings button that is placed on the bottom left, go to loader settings, then set gamecube mode to Nintendont.
Go back to custom paths and set this parameters:
Gamecube path to usb1:/games (don't touch if is this is already the default option)
Gamecube Nintendont loader to sd/apps/nintendont (don't touch it if is already the default option).
Then put your game in a subfolder (named with the name that you prefere) of usb/games and rename it to game.iso
Every single game must be under a different folder, and every game in these different folders must named game.iso
Example:
Usb/games/supermariosunshine/game.iso
Usb/games/super_smash_bros/game.iso
Usb/games/imtoolazytoselectafoldernameformetroidprime/game.iso
If the game has two discs (like Resident evil rebirth,mresident evil 0, enter the matrix,mresident evil code veronicq ecc.) You need to put the iso of the second disc in the same folder with the name disc2.iso.
Once you have done that, the games will appear on usb loader gx qnd you cqn boot them.
-snip-
How do I put the meta/titles into the folder? I downloaded the icon one but I can't see how to download the others....it just says raw, blame, history etc. Am I missing something?