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...