These two functions accomplish two different things. wp_footer() is a hook used in your footer.php template file to ensure that the right code is inserted (from the core/plugins/etc) into the right place. get_footer() is used in your other template files to call for the code in your footer.php template file.
So in simpler words wp_footer() gets other code that you most likely don’t produce (but need), so it’s a little more abstract. get_footer() grabs the exact code that you wrote into your footer.php file so it is the WordPress version of PHP’s include() function.
Hope this helps 🙂