This book will not make you an expert on dragonflies. It does give you sufficient information on them to help understand what you see when you view them in the field. And it helps you identify the most common ones in the USA and Canada.
A few pages in the front of the book give brief background information on dragonflies, and on equipment and strategies for observing them in the field. Then you go to page after page of species descriptions. Important identification information is given for each species, and at least one (sometimes more when appropriate) photo. The photos are usually of good quality both as photos and as identification aids.
A key in the inside cover of the book helps you pick out characteristics of a dragonfly you are observing, and the key then points you to the appropriate pages in the book using a color tab system.
I compared copies in hand of this book, and its chief competitor, DRAGONFLIES THROUGH BINOCULARS. I felt this book would be more useful in the field, so I ordered this one from Amazon.com, not the binoculars book. That's the best testimony I can give. I've since read and begun to use the book, and I am happy with my choice.
Only downside to this book is that it may tempt you to order one of the larger, more in-depth books on dragonflies, which are quite expensive!