Below is a basic content projection example. Content project allows you to inject a component from parent to its child.
Parent component passing an h1 tag to app-test:
<app-test>
<h1 class="custom"> Ca va? </h1>
</app-test>
Child component, with ng-content where projected/injected content is rendered
<ng-content select=".custom" />
In the example, select is used to select the component that has a custom class. You can remove this selector. This is just to demonstrate you can select which components to render.