After having used Angular CLI and its basic command set, let's review the key parts of the app you just created.

• main.ts: This is the main entry point, which takes care of bootstrapping the entire application:

 platformBrowserDynamic().bootstrapModule(AppModule)
   .catch(err => console.log(err));

• app.module.ts: This is the root application module, which contains the app-level functional units. While modules are explained in detail in the Modules section, pay close attention to the fact that this module currently declares a specific component, the AppComponent.
• app.component.ts: This is the root application component that is included as part of the root application module (AppModule). Components are explained later in this chapter—for now, consider this as the root UI component that contains the entire app component graph within it.