This book is an excellent introduction to the D5100. The author begins with a chapter in which he gives 10 tips to follow from the very outset, and he explains the reasons for each tip. The chapters continue in a logical progression, one topic at a time, with assignments at the end of each chapter to give you a chance to apply what you have learned.
The book is aimed at users who are new to using a dSLR or have some knowledge but are looking to improve their skills. It's clearly written, and it focuses on the things you need to know in order to get the most out of your camera. It is not a comprehensive guide to every feature of the D5100 and it doesn't claim to be, and for me, that is its real strength. Instead of feeling frustrated or overwhelmed by too much information, the reader can work through the material at his or her own pace. The author offers enough to get you started shooting right away, then he goes on to explain the "professional" shooting modes (aperture priority, shutter priority, and manual mode), and he does it in a way that is accessible to anyone. He even tells you which shooting situations make the most sense for each mode.
The book focuses primarily on using the D5100 for still photos, so the section on video is short and to the point. There is more information in two bonus chapters offered for free online at the publisher's website, but I have not had the need to access them yet.
The book includes many photographs with shooting data and analysis, as well as detailed photos of the camera itself, identifying all of the controls, and also many screenshots of the LCD menu to show exactly how to adjust various settings.
To call this book "user-friendly" is an understatement, and the author is to be commended for writing a book that presents a good amount of information in a way that any reader will find accessible and enjoyable.
I own several other excellent books about the D5100, and I refer to all of them, but this is the one that got me started and if I had to recommend just one, this would be it.