This action is used to add extra submenus and menu options to the network admin panel's menu structure. The network admin panel is only seen by a super admin in a multisite installation.
The function associated with this action runs after the basic network admin panel menu structure is in place. For example, the function might call add_submenu_page to add a sub menu page.
<?php add_action('network_admin_menu', 'function_name'); ?>
where "function_name" is the name of the function to be called.