Which function required?

Add

<?php get_footer(); ?>

into index.php or the template you are using

Then create footer.php and add in something like this:

<?php
    /* Always have wp_footer() just before the closing </body>
    * tag of your theme, or you will break many plugins, which
    * generally use this hook to reference JavaScript files.
    */
    wp_footer();
    ?>
    </body>
</html>