This book is primarily intended for intermediate to advanced PHP developers looking for a way into Magento module development. The existing Magento developers might find certain chapters interesting as well, depending on their previous experience.
This book will give you enough insight into the structure and concepts, and teach you a few tricks that will help you master Magento more easily. By the end of the book, you should familiarize yourself with configuration files, models, blocks, controllers, event/observers, shipping, and payment methods. All of these should form a solid foundation for your developing modules later.