Watch the Add A Voice online guitar lesson by Brad Carlton from Chord Studies: Evolving Progressions Vol. 2
Here we're taking the previous lesson, which was Dm7 to G7, and we're adding another voice. We're keeping a G up on top so G becomes the first voice now, giving us a Dm7/11 to a G7. It's as simple as that - adding another voice to a progression you already know.