From the top frame loop editor:
Select the blue “Add Slides +” button. From the drop-down menu, pick the “Create Slide” link to make the new slide.
This opens the slide templates library. Here you’ll see there are many types of slides you can make. Select “Message.”
Type in your message. Long messages will scroll across the screen.
Hit the blue “Save” button. Now you will see the message slide in your loop list.
You can grab the new slide and drag it to the position where you want it play in your loop.
If you want to display more than one message, add more by continuing to use the “Add Slides +” button.