Wordpress - Create Widget in functions.php and adding it to the theme

footer.php

<?php dynamic_sidebar( 'footer_menu_widget' ); ?>

functions.php

// Add Footer Menu Widget
function footer_widgets_init() {

	register_sidebar( array(
		'name' => 'Footer Menu',
    'before_widget' => '<div class="footer-menu">',
    'after_widget' => '</div>',
    'before_title' => '<h3>',
    'after_title' => '</h3>',
	) );

}
add_action( 'widgets_init', 'footer_widgets_init' );