The Instruction says...
2. Download the Tag Feed plugin file.
3. Unzip the file into a folder on your hard drive.
4. Upload tag-feed.php to /wp-content/
Most plugins are uploaded to /wp-content/plugins/.
This plugin MUST be uploaded to /wp-content/ using FTP.
In the plugin there is a file global-tag-feed.php
and a subfolder named includes.
What are they for?