The Router-Link, RouterLink-Active and Router-Outlet are directives provided by the Angular RouterModule package. It is Provides the navigation and URLs manipulation capabilities.
Router-outlet directive: - Router-outlet directive is used to render the components for specific location of your applications.
Both the template and templateUrl render the components where you use this directive.
Angular2 - Routing Concepts
|What is Routing in Angular 2?||What is Routes?|
|What is Router Imports?||What is RouterOutlet?|
|Is it possible to have a multiple router-outlet in the same template?||What is RouterLink?|