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Out of the box, Drupal 8's top horizontal menu is flat. To view the contents of each section, you need to click on a menu link in the menu, which then takes you to a page filled with the appropriate links for each section, like a switchboard.

This can be a fairly time-consuming way of navigating for site workers.

This is where the Admin Toolbar comes in...

Click on an image to make it bigger.
D8 Structure - Enable Admin Menu - Navigate to Module List

1. Navigate to Module List

Up in the top menu, click on the Extend link.

D8 Structure - Enable Admin Menu - Module List

2. Module List Overview

The module list on the Extend screen displays every module in use on the site, both core optional and contributed.

D8 Structure - Enable Admin Menu - Enable Admin Toolbar

3. Enable Admin Toolbar Modules

In the filter field, type admin tool.

All of the items that have this in their titles will appear.

Select Admin Toolbar, Admin Toolbar Extra Tools, Admin Toolbar Links Access Filter.

Click the Install button.

D8 Structure - Enable Admin Menu - Admin Toolbar Confirmation

4. Enabled Module Confirmation

A confirmation message will appear, informing you that your modules are enabled.

D8 Structure - Enable Admin Menu - Drop Down Menus Available

5. Test Admin Toolbar

Hover on the top menu to test your new Admin Toolbar out.