I figured it out.
When you set the event for the sound file to play, a small window pops up for setting the sound parameters. The bottom field in that window is where you have the option to set the tag.
The tag doesn't have to be anything in specific, like the name of the song in your folder.... it can be any name or code you want. Want to reference a song called Planting Tulips? Give it a tag called donkeyBreath, & whenever you want that song to play, just create an event that plays the song that has the donkeyBreath tag.
I imagine this would be useful for playing groups of sounds, like if you have a sound for a missile hitting an enemy & another one for the enemy screaming....you could give both sounds the tag called missileHitsEnemy, & then make a single event that could trigger them at the same time.