What Is Router imports?
It is an optional service that presents a special component view for a given URL. It has own library package- @angular/router and It is not a part of an Angular core.
The Angular package looks like this.
import {Routes, RouterModule,}  from '@angular/router';
And
  //Composability and Grouping
  //imports used for composing modules together.
  imports: [
    BrowserModule,
    //enableTracing enables debugging purposes only
    //useHash enables the location strategy that uses the URL fragment instead of the history API.
    RouterModule.forRoot(appRoots, { enableTracing: true, useHash:true })
  ],
For
more detail kindly refer the link - https://www.code-sample.com/2018/05/angular-5-6-7-routing-and-navigation.html