Adding widget to Wordpress

add_widget.php

in functions.php:

//add a widget area in the header as described by TomHart
if ( function_exists ('register_sidebar') )
register_sidebar( array(
  'name' => __( 'Header Widgets Area', 'twentythirteen' ),
  'id' => 'sidebar-header',
  'description' => __( 'Header widgets area for my child theme.' ,  'twentythirteen' ),
  'before_widget' => '<aside id="%1$s" class="widget %2$s">',
  'after_widget' => '</aside>',
  'before_title' => '<h3 class="widget-title">',
  'after_title' => '</h3>',
) );

in header.php:

<?php if ( !function_exists('dynamic_sidebar') ||
!dynamic_sidebar('Header Widgets Area') ) :
 endif; ?>