Add angular selector as Custom HTML Tag
Add selector name as below inside a double quotes in your component ts file
test.component.ts
@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})app.component.html
<div > <app-test></app-test> </div>
Add angular selector as Class
use ” . ” in selector to use it as class
test.component.ts
@Component({
  selector: '.app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})app.component.html
   <div class="app-test" > </div>   
 Use as Attribute
Add “[” “]” tp selecter as below
@Component({
  selector: '[app-test]',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.css']
})<div  app-test> </div>