This chapter will teach you everything you need to know to get started with Lisp. I'll cover all of the core features of the language. I encourage you to think of this core as the Lisp language itself, and everything else as a very large standard library. With this background, you'll be much better equipped to learn the rest of Lisp, either by reading the rest of the book or via a reference manual such as Common Lisp: The Language, 2nd Edition.
You should read this chapter all the way through. At times, I mention other chapters and later sections of this chapter, but you shouldn't have to follow these references to understand this chapter. When you finish this chapter, you should work through Chapter 4 while sitting at the keyboard of your Lisp system.