Watch the Melo-G online guitar lesson by Brad Carlton from Chord Studies: Slash Chords Vol. 1
This is a I-V/I-VII-V progression in the key of C. Our slash chord here is the V/I chord, G/C. Our first chord is a standard C chord with the high G note tacked on top. Release fingers one and two and you'll have the G/C chord. We move to an Am7 chord and you'll notice we are keeping that G note on top throughout. This continues as move to the V chord of the key, G.