Chapter 1, Get into Shape with @NgModule, discusses the @NgModule decorator, which clearly defines a segment of functionality in your app . This will be the organizational unit of your project. Before you begin building your app, you will gain many benefits by taking a moment and thinking about the various units/sections/modules that you may need/want for your app.
Chapter 2, Feature Modules, teaches you that structuring your app with feature modules offers many advantages for maintainability in the future and reduces duplication of code throughout your app.
Chapter 3, Our First View via Component Building, actually lets us see our app for the first time, where we need to build a Component for our first view.