How can I add the rooms created into a dashboard? I created all the rooms and now I want to create a dashboard with each room but it looks like I will have to create them from scratch again.
This may change in the future; Rooms is pretty new, and the release notes state that the current implementation is just "foundational." With that said: what you see now is normal--they are not accesible from Dashboard, so if you want to somehow group devices in Dashboard, you'll have to do that yourself however you want to (by row/column, separate Dashboard, etc.).
Right now, the main purpose it serves is to populate the "Devices" tab in the mobile app (not to be confused with the web/admin UI). Even there, you won't currently see all device types--just things like switches and bulbs. The only other thing it really does is populate the "Rooms" page in the admin UI (which you can also use to categorize devices into rooms in the first place, though the device page also works), which I suppose some people may prefer over the admin UI "Devices" page in some cases.
But again, this will likely change in the future as they add more features to Rooms and figure out more ways to make use of the "Rooms" concept itself.