USB loaders are just an application you run through the Homebrew Channel or as a distinct channel themselves. They require a custom IOS installed on your Wii to operate.
Simply having isos on your hard disk will now work, they need to be loaded using WBFS manager.
Twilight hack (normally) is a run once hack that allows you to install the Homebrew Channel. So you are not running it.
You'll find plenty of info in the tutorials section and there also is a whole forum near enough dedicated 'Software Backup Loaders'
Enjoy your learning journey.