Starting with the HttpClientModule

You need to import the HttpClientModule in app.module.ts by adding the following to the file:

...
import { HttpClientModule } from '@angular/common/http';
...
@NgModule({
...
imports: [
... ,
HttpClientModule
],
...

Having imported HttpClientModule into the AppModule, you can inject the HttpClient into an application class as shown in the "Updating the Dish service" page.