You can preview content even if you do not have a display currently available. This is a great option if you want to explore the presentation templates and schedules to see what they might look like on a Virtual Display, while waiting for a physical Display to be set up.
First, make sure you have created one or several presentations, and make sure they are assigned to a schedule. Refer to this article on how to publish content do learn how to do that.
Next, go to your Displays tab, and select Add Display. Further down the page, select Preview Virtual Display:
A Virtual Display will now be created. Be sure to select a Schedule from the lower-left of the page to decide what gets shown in the Virtual Display: