Use a file manager app to copy or move the mp3 or wav file to the Notifications folder. The next time you want to choose a notification tone, it should show up as an option.
Where is the music file located? Use your file manager app to locate it in that folder. Then select the music file and use the Copy function. (I don't use Cheetah, so I can't tell you the exact steps.) Now find the Notifications folder, and paste the file there.