Get content from one page and show it on another page

First off: The ID of a post or page is always an integer. “about” is either your about page’s title, slug or both.

Including the following in your “homepage’s” page template or in the sidebar combined with conditional tag(s) will display the about page’s content:

<?php
    // query for the about page
    $your_query = new WP_Query( 'pagename=about' );
    // "loop" through query (even though it's just one page) 
    while ( $your_query->have_posts() ) : $your_query->the_post();
        the_content();
    endwhile;
    // reset post data (important!)
    wp_reset_postdata();
?>

Edit: The above works, IFF your page’s slug is indeed “about”, otherwise adjust accordingly.