Watch the Drifting online guitar lesson by Andy McKee from Musicarium Songbook
The first tune is "Drifting", inspired by the playing of the guitarist Preston Reed. The song features some unusual percussion, and the left-hand is playing above the guitar neck through most of the tune to play chords as well as facilitate some of the percussive ideas on the upper part of the guitar body.
This piece is in DADGAD (from low to high), so the sixth string goes down to D, second string down to A, and first string down to D. This creates a Dsus4 chord, and is somewhat of a common alternate tuning, used exclusively by guitarists such as Pierre Bensusan
During much of this song, the left hand is above the guitar neck, similar to something Preston Reed would do. This allows you to hammer on chords, similar to how you'd play power chords while in drop D tuning. Place your thumb on the back of the neck and stack your index and middle finger on top of one another to get more strength, and just hammer them. This may look cool, but the main reason to do it is so you can hit the top of the guitar body as well to take advantage of the great clapping noise it makes. The right hand is also doing some percussion and tapping on the bottom of the guitar.