Go to the home page by clicking the Short.cm hyperlink in the top-left corner.
To tag Short URLs, you need to open edit setting of URLs. To do this click a pencil, next to the copy button.
The opened window has add tag option under Tag Short URL title. Create the tag you need, or use the one which has already been created by you and submit the change.
You can add as many tags to your Short URL as you need.