How to suppress template-parts in undescores?

First of all a simple advice if you are a complete beginner: i suggest you start from scratch with a tutorial that step by step takes you to create a theme. That way you will have a better understanding on how it works. Underscores is great i use it my self but if you are a total newbie, it could be more difficult to start with.

Do you have WP_DEBUG set to true in your wp-config.php file? If not go on the main directory of you WordPress install and add

define('WP_DEBUG', true);

It will allow you to see errors and help you identify what is the problem.
Here i reproduced my working page.php using Underscores

<?php
/**
 * The template for displaying all pages
 *
 * This is the template that displays all pages by default.
 * Please note that this is the WordPress construct of pages
 * and that other 'pages' on your WordPress site may use a
 * different template.
 *
 * @link https://developer.wordpress.org/themes/basics/template-hierarchy/
 *
 * @package sample
 */

get_header(); ?>

<div id="primary" class="content-area">
    <main id="main" class="site-main">

        <?php
        while ( have_posts() ) : the_post(); ?>


            <article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>

                <?php // YOUR CONTENT AND TEMPLATE for PAGES GOES HERE ?>

            </article><!-- #post-<?php the_ID(); ?> -->



            <?php 
            // get_template_part( 'template-parts/content', 'page' );
            // as you can see i just copied the content of content-page.php here
            // and commented out the get_template_part function
            // you can delete this, it is just to explain a little more ;)
            ?>

            <?php

            // If comments are open or we have at least one comment, load up the comment template.
            if ( comments_open() || get_comments_number() ) :
                comments_template();
            endif;

        endwhile; // End of the loop.
        ?>

    </main><!-- #main -->
</div><!-- #primary -->

<?php
get_sidebar();
get_footer();