In the next three chapters, you are going to focus on learning the Swift language. You will not learn everything you want to know about Swift, but you will learn enough to get started. Then, as you continue through this book, you will learn more Swift as you are learning Cocoa development.
If you do not think you will be comfortable picking up Swift at the same time as Cocoa development, you may want to read Apple’s Swift tutorials first. You can find them at developer.apple.com/swift. Or you can start with Swift Programming: The Big Nerd Ranch Guide (available Summer 2015).
But if you have some programming experience and are willing to learn as you go, then you can start your Swift education here.