multiple menus

// Register Navigation Menus
function custom_navigation_menus() {

	$locations = array(
		'left menu' => __( 'left menu', 'text_domain' ),
		'right menu' => __( 'right menu', 'text_domain' ),
	);
	register_nav_menus( $locations );

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