Some of the most powerful tools in Photoshop are the Selection tools. They enable you to edit selectively.
Try to develop a feel for when you can use selections. They can save you a great deal of time when you need to fill a space with color or an image, when you need to manipulate just a piece of an image, when you want to selectively brighten or adjust part of an image, or when you need to extract a piece of an image from a larger work.
The book refers to selections throughout the remainder of the chapters, so if you need to, dog-ear a page.