Assuming you have the following pages:
- Home
- About us that has a slug of
about-us
And you want to display the content of the About us page into the Home page.
<?php
$about_us = get_page_by_path('about-us'); // supply the page slug; i.e. about-us
$about_us_content = get_the_content($about_us->ID);
?>
<div><?php echo $about_us_content ; ?></div>
Alternatively, you can use the get_page_by_title to retrieve the post using its page title