frontend/controllers/CollectionController.php

<?php
    
    namespace frontend\controllers;
    
    use yii\web\Controller;
    
    /**
     * Article controller
     */
    class CollectionController extends Controller
    {
        
        /**
         * Displays article list.
         * @return string
         */
        public function actionIndex()
        {
            return $this->render('index');
        }
    }