If you aren't on Facebook yet, why not? If your excuse is that you don't understand it, then Facebook: The Missing Manual is the book you must read. This book is written for the beginner, and it really does give you a great step by step map to setting up your Facebook account. Not only is this book in plain English, it also has great illustrations to show you exactly how to do each thing. It also explains all the different functions you can do with Facebook. It'll teach you how to chat, how to reply on somebody's wall, and how to install different applications (just to name a few things). As a user of Facebook myself, I even learned a thing or two while reading this book.
Facebook: The Missing Manual is a great beginner book for Facebook.