title: UIScene concept is not clear
body: <p>Before we all get used to the approach when in <code>AppDelegate</code> we create <code>UIWindow</code> and then set <code>rootViewController</code> for this <code>Window</code>. Sometimes when we needed to have a custom alert we can create a new <code>UIWindow</code> that will be above.</p>
  
  <p>Now Xcode automatically creates <code>UIScene</code> and creates <code>UIWindow</code> base on this scene. I would appreciate if somebody can explain in details how to use this scenes in real life and what is their major benefit from using just <code>UIWindow</code> in <code>AppDelegate</code></p>
  
  <p>Because this <a href="https://developer.apple.com/documentation/uikit/uiscene" rel="noreferrer">article</a> doesn't explain much </p>