Ionic app execution in mobile

which file run firstly after app install in mobile
(step by step execution of ionic app )

If you want to know where you should so basic stuff at app startup like setting the language, check login data, etc. it is normally the app.component.ts in the then() Block of the device.ready() Methode.

how to know ionic app to which file run first

That’s really simple. The base html File is the index.html. As you can see there the body is something like this:

<body>
  <app-root></app-root>
</body>

The <app-root> is the main selector, that you can see on top of the app.component.ts:

@Component({
    selector: 'app-root',
    templateUrl: 'app.component.html',
    styleUrls: ['app.component.scss']
})
export class AppComponent implements OnInit {

that means index.html file run before app.component.ts

You must understand what an ionic/cordova app is. It is a native app, that only provides a Webview. In this Webview your Angular Code is running. That is why it works for more platforms with a single code basis. Every website has a base File, the index.html. This laods the app-root Component which is the base Component, where you can initialize the App.