1. First create a angular project using angular CLI without a routing module
Make the application understand how to construct the URL while navigating by adding <base> tag inside the <head> tag on index.html
<base href="/">

2. Create a file name “app-routing.module.ts” inside the app folder
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
const routes: Routes = [];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }
3. import AppRoutingModule in app.module.ts file and also add it in the import section in @NgModule decorator

Note : We can create a project with routing functionality directly while creating a angular project using angular CLI command
ng new project --routing
Note : We can also add routing to an existing project with below command :
ng g module app-routing –flat –module=app