I do not understand how you can earn the Tag Editor badge. What do you have to do and where?
When you click on a tag (such as the ones visible under this very question — support, badges, and edit-badges), you will see a short excerpt from the tag's "Tag Wiki", which is a short description of what that tag is for and how it relates to the site:
Beneath that excerpt is a link titled "edit". It is on this page that you'll be able to improve the description of a tag in order to earn this badge.