Within Teamwork.com, you can enable tags on your site and specify whether non-administrators can create tags.
Click your profile icon in the bottom left corner of your site and select Settings from the dropdown menu.
In the settings area, go to the General subsection.
You will see an option to Allow tags to be used on your site. You also have an option to lock the editing of tags to administrators only.
When you enable the tags option, you will also see a Tags area in the site settings menu for managing tags.
For more information, see: Tag Options