I completely understand, it was quite difficult for me to grasp the first several times I read the book and I still don't feel like I have a great understanding of it.
I think for me personally, it's helped me think about drawing the figure in a different way. In the first few pages of the book, he writes about the "humanity of the figure", and some parts of that really stuck with me. I've also watched some videos of him demoing his process, and that's really made me think about how gravity, weight, etc affect the pose, and how the model is in motion (even though it's a photo). Another few things he emphasized that stuck with me are to really loosen up, "be passionate about the aliveness of the model and the pose", to not worry about the drawing, and to "always have something to say" (don't just copy, think critically about what to exaggerate or emphazise. In the book, he calls it "having opinion").
I'll likely reread the book a few more times, but I hope this helps in some way.