If you are responsible for the administration and implementation of the system, you should generally read this book sequentially, from the beginning to the end, because it will guide you through the entire process of preparing the system and successively introduce various aspects of the use and administration of the system.
End users should primarily read Chapter 1, Introduction, Chapter 3, Working with issues and Chapter 4, Tracking issues, which introduce the basics of working with the WebIssues system.
If you are an advanced user and want to start working immediately, you can read this book in whatever order you want. To find information about the topic you are interested in, use the Table of Contents included at the beginning of this book.