RE: Transition to Unified Interface
Hi,
Apps are different concept than solutions. Apps can be part of one or multiple solutions, and these solutions are used to deploy customizations from one environment to another.
To simplify, think of solutions as technical containers of customizations and think of apps as role-based containers of User Experience.
From the screenshot you are showing, it looks like you only have one entity in your sitemap.
You can in fact add any entity from your environment to the sitemap of your app (regardless of if they are part of the solution your app is part of).
Once you've organized your app navigation, don't forget to Save to Publish, so that your customizations gets reflected after a browser page refresh (F5):
It might actually be easier if you started by Microsoft provided first-party apps (such as Sales Hub or Customer Service Hub, depending on your business requirements and license plans).
You can get them from Microsoft AppSource, for example for the Sales apps:
Dynamics 365 Sales, Enterprise Edition App
Dynamics 365 Sales, Professional
You can also add new solutions to your environment through the Dynamics 365 Administration Center: https://port.crm.dynamics.com/G/Instances/InstancePicker.aspx?redirect=False (make sure you replace the crm* with the right number as in your environment URL, if appropriate. For example for the Europe region, it's crm4).
From that page, you can go to an environment and add solutions: