If Else
aboutus.component.ts

export class AboutusComponent implements OnInit {
  showMsg: boolean = true;
  .
  .
  .
}

aboutus.component.html

<p *ngIf='showMsg; else elseBlock'>aboutus works from If block!</p>

<ng-template #elseBlock>
    <p>aboutus works from else block!</p>
</ng-template>

Output

aboutus works from If block!

Switch Case
aboutus.component.ts

export class AboutusComponent implements OnInit {
  .
  .
  color : string =  'pink';
  .
  .
}

aboutus.component.html

<div [ngSwitch] = 'color'>
    <p *ngSwitchCase="'blue'">Its Blue Color</p>
    <p *ngSwitchCase="'red'">Its Red Color</p>
    <p *ngSwitchCase="'green'">Its Green Color</p>    
    <p *ngSwitchDefault>Its Default Color</p>    
</div>

Output

Its Default Color