This arrangement has the melody played in the key of C. This is where the Carter Family recorded it. The melody follows the syllables of the song as you would sing them. Pay close attention to the right hand fingerings. Learning to sing the words as you play them can greatly help with your memory and internalizing many musical elements naturally. Even if you're an experienced player start with the basic melody and memorize it. There's enough licks to create a wide variety of Scruggs and 3 finger style arrangements of this song.
A lot of the three finger licks demonstrate some very cool chordal movement that incorporate the melody, and of course the Scruggs style licks show you some examples of how Earl may have interpreted this classic melody. Pay attention to the little dots that show above some notes. These are staccato markings. They mean to play that note short. You release finger pressure on the fretted note just after playing it to deaden the sound.