From what I have heard(!), those books work sort of like those
really old multiple choice computer games, where you choose an action and the book then tells you to "go to page X to see what happens next".
You know:
You encounter a hulked figure hiding in the shadows! What do you do?
- Approach the figure to confirm its identity.
- Open fire with your trusty lasgun.
- Run away!
Obviously with more fancy writing and detail.