How to link to a custom .php page in my folder

Question

WordPress doesn’t load templates that way.

First: give the template a name:

To load a page template, first you’ll have to make sure your template has a name. To do that, you’ll have to have the following CODE in your template file (here mypage.php):

<?php
/**
 * Template Name: My Page
 */

Once you have the above PHP comment, WordPress will recognise it as a template file.

Then, assign the template to a page:

Now you’ll have to create a WordPress page (from wp-admin).

While you create the page, WordPress will give you the option to choose a custom template (if there is one). After you choose the template and Publish, that page will use your mypage.php file as a template.