How the Angular app start

1. main.ts file will be executed first, where there is a function, called bootstrapModule(AppModule), that will connect the module in the argument.
2. this module should be a module created by angular, in this module (AppModule) (app.module.ts), it points out bootstrap component (AppComponent) (App.Component.ts)
3. this component has defined the selector (app-root), and will connect html template (app.component.html) to render the content of this file