Your home screen and the first page you will see when you open Marvin is the "My Day" view. 

Whenever you navigate to some other parts of Marvin (e.g. Master List, calendar, super focus mode, etc.) they open up in a fullscreen overlay on top of your main view.

To exit out of an overlay and return to your home screen you can either press the "esc" key on your keyboard (top left) or click the "x" on the top right of the overlay.