"app://" - URI scheme, tells the OS how to handle the request (app launcher).
"80C...891" - App's ProductID GUID. Unique for every app (but does not change on updates). Identifies the app in question.
"/_default" - Use the app's normal launch task (as opposed to a launch task for a live tile or something).
"#" - URI fragment indicator, specifies where within the app to navigate to.
"Microsoft.Mcx.Mobile.UpdaterShell" - Name of the assembly containing the desired XAML file (the specification method is WP standard for embedded resources).
";" - Separator between the assembly and the path within the assembly; standard in WP.
"component/Views/" - Path to the embedded XAML view that you want to open (also WP standard format for embedded resources).
"AdminView.xaml" - the name of the (embedded) XAML file that you want to open.
Hope that helps.