Answer
Set SelectionMode to Single or Multiple, then bind SelectedItem (or SelectedItems) and handle SelectionChanged, or bind SelectionChangedCommand. In MVVM you typically bind SelectedItem to a view-model property and react in its setter or via a command, avoiding code-behind.
<CollectionView ItemsSource="{Binding Items}"
SelectionMode="Single"
SelectedItem="{Binding SelectedItem}"
SelectionChangedCommand="{Binding OpenCommand}" />Real-world example Tapping a row in a contacts list sets SelectedItem, which the view model uses to navigate to a detail page via its command.