Ok then. We begin our journey through these 4 chords with a simple Asus4! I've chosen this voicing because it sounds very "in-between", and can be easily tweaked to serve as a platform for both major and minor playing. It's best that you listen to the video, rather than try to be over-analytical about the whole thing. Sound and perception of harmony is key here, not what theory might or might not dictate as being "correct". Just listen through the video, and then head on to the backing track for Part 1, and try out the scales for yourself!