How to add the Recent Items stack (block)
You didn't mention which CMS you are using, and this is CMS-dependent feature. In Drupal, for example, you would select from the menu Structure | Blocks and then find the item labeled "CiviCRM Recent Items" and select "Sidebar First" for its region for the theme that you are using for CiviCRM (which can be different for admins, and there is a setting at bottom of /admin/appearance to set that).