Watch the Happy Moat: 5 online guitar lesson by Pete Huttlinger from The Lone Arranger

The thumg starts alternating the bass notes on the 6th and 4th
strings. This is a must for anyone who plays fingerstyle guitar. A whole new world opens up when you
can alternate consistently while playing a melody. If you need help with this technique, try my tune
called Darcy's Guitar.