Old-school as they are, tags are still one of the best methods for keeping track of similarly-themed songs.
A tag is a keyword description of a song that makes it more easily searchable. Tags can be added to songs projects are searchable from the search form in your catalog. They're an easy way of grouping certain songs together, as well as differentiating similar songs from each other.
To add a tag:
Go to the Lyrics & Recordings tab of a Song Project.
At the bottom of the page is a text box labeled "Tags".
Enter any keyword you'd like in the box and press Return.
The tag has now been added to your song! To delete a tag, simply click on it.