Directions on how to tag a product in Magento administration (not intuitive):
1. Go into Catalog > Tags > All Tags. 2. Add a tag or use an existing tag as desired.
3. Click on the table row for the tag.
4. Open Products Tagged by Administrators.
5. A list of products with the tag will appear.
6. You can remove the tag from any of those products by unchecking the checkboxes.
7. To add the tag to another product, click Reset Filter.
8. A list of all products will appear.
9. Check the checkbox to add the tag to a product.
10. Click Save Tag in the upper right.