"App.xaml" contains the class code that initialises the project and is the logical equivalent of main().
Effectively the app’s main method. The plumbing that makes it the app’s entry point is enabled by an “Entry point” setting in the package manifest (on the Application tab). When you create a project, Visual Studio automatically sets it to the namespace-qualified name of the project’s App class.
Enables the frame rate counter overlay in debug mode, navigates to the app’s first page, and calls Window.Current.Activate to dismiss the splash screen. If you want to add a new page and make it be the starting point of the app, or if you want to customize the initialization logic, this is where you can do it.
Attached to the base class’s Suspending event. This gives you an opportunity to save state before your app is suspended, although the generated code does nothing here other than provide a TODO comment.