Here are only a few books about using CMMI that are available to help you get started:

Real Process Improvement Using the CMMI

(May 2008) This book presents readers with non-academic, real-world approaches to process improvement via CMMI. The author provides concepts and techniques for CMMI-based process improvement which are as effective as they are innovative. Using plain language and enlightening illustrations, the author identifies the most critical concepts of the CMMI, and explains how to turn those concepts into real process improvement.

CMMI Distilled: A Practical Introduction to Integrated Process Improvement

(June 2001) This book provides a concise introduction to the CMMI product suite, highlighting the benefits of integrated process improvement, explaining key features of the new, integrated approach to process improvement, and suggesting how to choose appropriate CMMI models and model representations for your organization.

Interpreting the CMMI: A Process Improvement Approach

(April 2003) This book provides you with specific techniques for performing process improvement using the CMMI. They walk you through the myriad charts and graphs involved in statistical process control and offer recommendations for which tools to use. The book covers roles and responsibilities, people issues, how to generate meaningful documentation, how to overcome resistance to change, and how to track the success of your efforts.

CMMI Survival Guide: Just Enough Process Improvement

(October 2006) With a proper guide to help navigate around unknown dangers, potential pitfalls, and false paths, you too can realize substantial business value from a successful CMMI implementation. This book is such a guide, full of the real-life examples to ease your way, and written in a lighter style to ease your reading.

CMMI: A Framework of Constellations for Building World-Class IT Organizations

(August 2011) This book is a thoughtful compilation of CMMI practice interpretations and software engineering principles, approaches, and proven techniques that help the reader internalize all three CMMI constellations.

Other books are available in the SEI Series in Software Engineering. You can purchase these and many other books about CMMI at most book retailers.