Rob Irving (AdDuplex Developer Advocate and Microsoft MVP) has written a great tutorial on implementing AdDuplex ads in App Studio apps for both Windows Phone and Windows. You can find it and follow the steps here: Adding AdDuplex ads to your App Studio App
The tutorial covers implementation of AdDuplex as a fallback solution for Microsoft pubCenter ads. In case you want to use AdDuplex exclusively you can follow Rob's tutorial to the point where he ads the AdDuplex control, but instead of adding it next to the pubCenter control, just replace it with the AdDuplex code.
I like