Sun Jianyun, Sun's daughter, says in the introduction that quite a bit can be learned from that book.

Though the English translation by Albert Liu is mostly unintelligible (even to my Chinese ears), you can still see Sun doing his thing.

If that book is going to be your textbook for this, I'd suggest starting with the beginning and going onward. It's hard to get through the curriculum, but the static pictures give some idea of what the stances are supposed to accomplish.

Personally, I do my Xingyiquan very different from Sun. This isn't because of lineage, this is because of functionality (i.e. fighting.) Thus, my postures are completely different from Sun's though the idea is the same.

If you can USE the stuff from the book in combat against a resisting opponent, you'll have gotten out of the book what REALLY needs to be gotten.