Learning Carbon is a gentle introduction to the very basics of Carbon programming. It carries the reader over the foothills of Carbon development to give them a solid grounding in the fundamental concepts of the API. This book will also be of some value to application developers who are already familiar with the classic Mac OS programming APIs but who need to know about the nuances and special flavors that the Carbon application framework adds to the Mac OS.
As other reviewers have pointed out, this document covers many of the same areas as Apple's on-line developer documentation, but the value of the text is that it collects that documentation into one place and ties it together into a cohesive tutorial. The text is also able to go into a little more depth on some topics than the on-line documentation.
If you're looking for a comprehensive reference text, this book is not going to help you, but if you need to know about the fundamentals of developing applications with the Carbon framework then this book can teach them to you.