Installed twig with composer require twig command.

src/Controller/MainController.php

@@ -2,14 +2,15 @@
 
 namespace App\Controller;
 
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\Routing\Attribute\Route;
 
-class MainController
+class MainController extends AbstractController
 {
     #[Route('/', name: 'main')]
     public function homepage(): Response
     {
-        return new Response('Hello World!');
+        return $this->render('main/homepage.html.twig', ['variable' => random_int(0, 1e10)]);
     }
 }