How to Register a menu in wordpress

********How to register a menu **********

//first past this code in function.php to register menu

		// register menu
		function erika_theme_menu() {

			register_nav_menus(array(
			'main_menu' => 'main menu'


			));

		}
		add_action('init', 'erika_theme_menu');



//than past this code in header.php, where you want to call menu


		<?php

		wp_nav_menu(array(
			'theme_location' => 'main_menu',
			'menu_class' => 'sf-menu clearfix list-unstyled',

		));

		?>