This book is part of the official courseware written by Digidesign. It forms the foundation for all further training in Pro Tools. Not only is the book reasonably priced, but this latest edition - updated for Pro Tools 8 - is full of illustrations, images and clear concepts. It introduces the basics of LE and HD systems, with nice clear systems diagrams. Pretty much all the important boxes are shown. In this way it has to be the most comprehensive and up-to-date book on the market. It touches on the basics of using Pro Tools - more depth is found in the "Pro Tools 110" courware - but you'll need to contact an approved Digidesign Training Partner to find get your hands on that book.
It's hard to imagine a clearer introduction to using Pro Tools for complete beginners. A accompanying CD contains samples projects for part 3 of the book and some video training.
It's important when learning Pro Tools to get a good introduction that covers the basics before you try to fly. In this way you'll get less confused when you come to do more complex thinngs. So, I would say, this book is a must for new beginners and those who missed out on a decent start with Pro Tools.
After reading this book you'll quickly want to progress to more advanced topics. The Digidesign documentation and other books may be of use by then.