How to proceed with the book "Pawn Structure Chess" by Andrew Soltis? Should I memorize everything in the book, or use it in some other way?
I'm not familiar with the book itself, but for learning pawn structures it isn't important to memorize every single thing. The key is to understand the general ideas behind each structure. E.g.: what are the main plans, which pawns are weaknesses, what squares work well as outposts for pieces, can the structure be changed as the game goes on, etc. 

Knowing these things would be useful if you were playing a real game with the structure in question. And the key is to know them, not to memorize them by rote. If you can understand why certain structures give rise to certain characteristics, then you could generalize when facing a new structure over the board.