You can access internal game music by typing its One True Name in the Play Song event, with no file extension. You don't need to input an offset value, they use internally stored data which should be correct already.
Note that levels using internal music like this will not work in the standalone version of the editor, since it doesn't have the music files included.
Internal tutorial music should automatically loop correctly in gameplay, though in the editor you will have problems when scrubbing beyond initial song length.
To stop it from looping, you can use the OneSongAtATime(true) custom method and play a new song, or allow multiple songs and use the
CurrentSongVol(targetVolume, fadeTimeSeconds)
PreviousSongVol(targetVolume, fadeTimeSeconds)
custom methods to fade them in/out.
Check the RDCode page for more info about these custom methods:
RDCode: Rhythm Doctor Coding (and other advanced mechanics)
“I have your name now,” I said softly. “I have mastery over you.” -- Kvothe, The Wise Man's Fear