If you want to get an instance of the view using MEF, you first of all need to Export the view.
So add the [Export]
attribute to your StartWindow class:
[Export]
partial class StartWindow : Window
{
...
Now, in your App
class use ImportingConstrutor to get the instance:
public class App
{
[ImportingConstructor]
public App(StartWindow window)
{
// Do whatever you need
}
Regarding good articles on MVVM, I recommend Josh Smith's blog