Hi Mirta,
You can't do any work with DPS 2015 unless you have either a trial account or a DPS subscription. None of the dashboard capabilities are available without either of those two types of accounts.
1) You need to build a preview app, and per what I wrote above you either need a trial account or a subscription.
2) The Adobe Content Viewer isn't used with DPS 2015.
3) You can if you want to test overlays, but honestly the desktop preview tool is so old it's not really a true reflection of interactivity in either DPS 2014 or DPS 2015.
4) The beta program ended over a month ago. You need to either get a trial account, which is valid for 30 days, or purchase a full license to DPS.
Neil