Hi,
if you are new to Linux you will have some work to do.
First we have some general conditions here:
http://forum.backbox.org/announcements/general-forum-conditions/You can find lots of informations, guides, tutorials etc. on the web.
Reading will be your main activity for the next months

Since the field is too large it's difficult to suggest some particular places, but if you search around you'll find everything you need. You can start from Ubuntu and Debian guides/tutorials. Use the beautiful
apropos and
man commands in the terminal to get manual pages on a tool/system related stuff.
Find 3, 4,...,10,...,100 guides on a specific subject. The things you don't learn from one, you'll learn from the others...
Also please, be sure to have learnt the basics before switching to using bbox tools, or you will find some difficulties. Hopefully you'll read something before, let's say about networking, systems, attacks, some programming knowledge and so on.
BackBox doesn't have a book (yet), because it's an ubuntu based distro, and what you need is tools documentation, which are provided by the tools developers as man pages and/or online docs. For system admin tasks you can refer to Ubuntu documentation. But usually using a search engine is enough to get nice stuffs.
Hope you'll have fun!

Bye!