start with in angular ngif code example
Example 1: ngIf else
content_copy
<div *ngIf="condition; then thenBlock else elseBlock"></div>
<ng-template #thenBlock>Content to render when condition is true.</ng-template>
<ng-template #elseBlock>Content to render when condition is false.</ng-template>
Example 2: ng if
<ng-template [ngIf]="heroes" [ngIfElse]="loading">
<div class="hero-list">
...
</div>
</ng-template>
<ng-template #loading>
<div>Loading...</div>
</ng-template>