David Holmgren and Bill Mollison worked together on the first ever book about permaculture - "Permaculture One". They are pretty much the founders of permaculture, so it sounds like you are starting in the right place. I haven't read any of Holmgren's later books.
I sometimes learn more or learn better from videos and from seeing things than I do from reading books. For me it was easier to learn what a swale was by seeing pictures or video of one instead of reading about it, for example. YouTube has tons of videos from Bill Mollison that I've seen, including an entire lecture series he did that was many hours long. Geoff Lawton also worked with Mollison and Holmgren, and he's got some really good videos out there as well. best of luck finding the information you're seeking.