Toolbar of wordpress administration screens

On the top of administration screen wordpress enable and show you a bar call Toolbar that it consists of the info of this CMS as quick access to other function like poset, and new page, edit page or post, links, and new plugin, user information, show you the comments, alerts new version of wordpress plugings, themes and make you easy switch from admin site to home page site. you can enable or disable it by this way: make sour you stay log on and go to administration screen, after go to user and than your profile link of left menu and find Toolbar and "Check" Show Toolbar when viewing site.
finally update your profile.

WP_Admin_Bar is class of CMS WordPress use for generating the Toolbar when you signed in you can lines the top of WordPress sites. It can be hooked and modified to remove or add options that appear in the administration  bar.

How to using this class:

It is used internally by WP to create $wp_admin_bar that is a object of it . Most modifications to WordPress toolbar will generally be done by modifying the $wp_admin_bar object that is passed through the admin_bar_menu hook.
Example:

add_action( 'admin_bar_menu', 'modify_admin_bar' );

function modify_admin_bar( $wp_admin_bar ){
  // you put you option to show on bar hare ..... 
}

Array Session