add a link to admin menu bar I want to add the link to tags i.e. /admin/structure/taxonomy/tags directly to admin menu so that it appears next to "Content" link present on admin menu. How to do it?
You can achieve using below step:


Go to Administration -> Structure -> Menus
Click on 'Add links' in 'Management' menu row
Add 'Menu link title' and 'Path' for menu item.
Set 'Parent link' for the menu item, so it would display in correct position.
Save the form


Update:

By default, Management menu be only dispaly to administrator or the user which has permission to view it. 

If you want to set any specific visibility permission, you can use Menu item visibility module.


  This module exposes configurable and extendable visibility settings
  for menu links. For example, if you want to create a 'My account' link
  that points to /user, both anonymous and registered users have access
  to the /user path, so both will see the link, even if anonymous users
  do not technically have an account. Using this module will allow you
  to only have your 'My account' link visible to registered users, and
  hide it from anonymous users.