<a href="<?php site_url(); ?>/mypage.php">Go to page</a>

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

<?php
/*
Template Name: Full-width layout
Template Post Type: post, page, event
*/
// Page code here...

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

get_template_part( 'some', 'file' );