You use two major scale patterns to play “The First Noël”: major scale patterns #1 and #4, discussed elsewhere. To begin, put your hand in 2nd position (with your left-hand 1st finger hovering above the 2nd fret). Then place your left-hand 3rd finger (your ring finger) on the starting note F# at the 4th string, 4th fret. Now, you’re ready to play.
Take a look at the following music. Notice that at bar 8 you switch positions, jumping up to 9th position between beats 2 and 3. Try to let that half note ring for as long as possible before making the jump, but don’t be late for beat 3! This mid-measure jump allows you to play the chorus of the second phrase an octave higher. The song doesn’t really do that, but this makes it more interesting. Plus it gives you a workout in different positions.
After playing eight bars in the upper octave, shift your hand back to 2nd position at bar 16 to finish out the last eight bars. Note that the last bar, like the first pickup bar, is incomplete. It contains two beats, which allows it to even out the one-beat bar that starts the song. You can repeat the song by mentally stitching together the first bar and the last as if the whole song were a repeatable loop.