Welcome to Android Central! The music has to be in mp3 or wav format, I believe. If that's the format your file is in, then use a file manager app (like ES File Explorer) to copy the file from wherever it is currently over to the Ringtones folder. Then go to the Settings>Sound menu to select Ringtones. You should see the new music file listed there. Sometimes, you have to wait a few minutes. You may even have to reboot the phone before they show up.