These are typically handled with "pauses" in the set list. You can go to Repertoire > Pause Names and enter names like "Introduce the Band" or "Plug the Merch," and optionally write more info in the Notes field.
Then when adding songs to your set list, you can add a pause, click the options button (three dots) for the pause and select one of your defined pause names. Then the pause name will appear in the set list and the notes will appear when you reach that point in the set list.