Hi Marzia,In order to preview your content in DPS 2015, you will need to
Enable Preview when creating or editing the app.Also when you’re ready
to view content in the preview app, click the Preview icon in the
Content & Layouts section of the Portal.The below article will describe
you a step by step way on how to achieve that :Digital Publishing
Solution Help | Preview content for DPS 2015Regarding building the app,
you shouldn't have any problem created the app using a trial
account.Make sure t...