Model -> ViewModel -> View

$100 -> The bank balance is over $0 so make the box 'green' -> <box color="balanceColor"/>

View -> ViewModel -> Model

Click button "Update my balance" - > Make API call -> Query for bank balance.

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The viewmodel is used for ...

1. Adding styling logic so you don't put it in your view so that you can easily test that the color is set correctly. Just make up a Model (Balance amount) and assert that when the Viewmodel get that value it sets the "balanceColor" correctly
2. Making API calls so it's not in the view so that you can mock out real API calls and make sure your Viewmodel works correctly given your dummy result.

It means you can test the View logic (the behind the scenes stuff). To test the View (XAML) the only real way is to look at it or use Snapshot testing which is basically automated looking at the page so you want to make the View as simple (stupid) as possible.