Drupal has a powerful system for classifying all content on the site. Editors are allowed to administer these categories. You can do so at by going to Administer -> Content management -> Categories from the navigation menu on the left (you must be logged in).

Once there, you'll see a table with three columns, "Name", "Type" and "Operations."

Name
This is the name of the category, also known as a vocabulary. Vocabularies will generally be handled by site administrators and as an editor you will usually not need to worry about these.

Type
This column tells you which kinds of content the vocabulary will apply to. For example, a vocabulary may apply to videos but not to stories. Or, it could apply to both videos and stories.

Operations
These are the links you can click to administer the site's categories. The "list terms" and "add terms" links are what most editors will be using.