Need some help with Books and Chapters please

I am looking at:
https://www.vaultwiki.org/books/User-Manual

and it appears there is a Book with Chapters, and the Chapters have Chapters.

I have tons of content that is FLAT:
http://www.blincmagazine.com/forum/wiki/BASE_Wiki:Index

I want to organize this content better so that it is easier to find which I think it is NOT right now.
Can you help me understand what I am missing to get this sub category navigation?

Say you have "Book A" and "Book B". Make "Book B" into a chapter of "Book A". Then all of "Book B"s chapters will be sub-chapters of "Book A".