Re: Giving access to user for one application only in Work stream
Each user has their own Work area and other users including RootAdmins do not have access. There is a security that can be modified. But I really don't think that you want users seeing each others work areas.
The video referenced above is great for showing you how to give stream access and then even app access within a stream. That is very useful.
I would recommend that you publish the app from the work area into a stream and then give access to who needs it to that stream.