Setting up navigation hierarchy
To setup the navigation hierarchy you just add new windows and navigations into the LAYOUT section. Everything is explicit and really intuitive, Windows can be moved or rearranged inside navigations. A Window can contain controls (UI objects) and objects (objects without a UI like databases, classes, http connections and so on).
Startup Window is important because it instructs your app about what is the first window to display at startup. If you do not set a Startup Window then you’ll need to setup it using the code. An appropriate point to setup a starting point could be the DidStart Application event.