After you've created your test app in Principle, it's time to show the world! (or at least some people to test it and provide feedback for you!)
(Your testers will need the Principle Mirror App to see your creation.)
You will be prompted to provide a URL for your prototype. As Principle prototypes are not URL-based, you'll need to create a location. The easiest way to do this is to put the .PRD files into Google Drive or Dropbox, using that URL.
The PRD file can then be downloaded by your tester from the public/shared Google Drive or Dropbox file that you've created and shared:
Next, the tester will tap "Open in Principle".
This will allow access via the installed Principle Mirror app, and you can get started with your study session!
(Note, this is easiest for a moderated session, so that you can help walk your tester through this process!)