First, remove your newly uploaded page through ftp.

1. Static content

If your have static content:

1. Go to Admin area and go to Pages section and add a new page. You may change the slug to my_page or any thing else (it should be an available slug and not already assigned to any other post or page)
2. Put your content inside the Editor section and use TinyMCE to make it look as your want. You may use h1-h6, Bold, Italic, put images and videos and more.

2. Dynamic content

If your have dynamic content needs:

2.1. You own the current theme

If you own the theme you may add your file to your theme:

1. Create a file named page-{slug}.php under your theme's root directory where {slug} is your page slug (maybe my_page which will be page-my_page.php) and you may access it like:

   www.site.com/my_page
   

2. put some inclusions to include common parts like header & footer into it:

   <?php get_header(); ?>
   <main>
       <?php
       if ( have_posts() ) : ?>
           while ( have_posts() ) : the_post(); ?>
               <h1><?php the_title(); ?></h1>
               <div><?php the_content(); ?></div>
           <?php
           endwhile;
       endif;
       ?>
   </main>
   <?php get_footer(); ?>
   

2.2. You use a default wordpress (2020 theme) or any 3rd party theme

If you do not own the theme, then you may consider creating a child theme and go to step 2.1 afterwards.