I see a Window1.xaml and its associated .cs file, which are the main window. Then there’s also app.xaml and app.xaml.cs. First, what is the point of App? It seems to be empty.
I’m assuming I should put local variables to the Window on its cs file, and variables related to the whole program on App?
You should MVVM. Start early, win often.
App.xaml and its code file are used for application-wide resources and code that needs to run on startup. You shouldn’t be putting anything in app.xaml.cs unless you need to.