"path" is the path to your game folder defined in the loader (you can edit the "base folder" where you place the games, so there's nothing specific, it's called "path", but the default location is "sd:/games/" or "usb:/games")
which gamecube loader are you using ?
DIOS MIOS, or Nintendont?
DM is old, Nintendont is newer and easier to use, has more compatibility, etc.
Read Nintendont's first post to get the information about the path and filename.
I'll just leave an example here :
usb:/games/Zelda Wind Waker [GZLP01]/game.iso
Another thing :
You are trying to follow direction and get help by reading information from 2012 !
You shouldn't trust old information without checking if there's no new version and hack and tools and everything else released since that time. It will prevent headache for you and for other users who will have to help you fix any issues due to following outdated guides.
what you need to keep from this thread is : gcm = iso, you can rename the file extension, then use your favorite (and newest) gamecube iso loader.