This project is compiled in Xamarin.Forms 1.2.2.6243. For iOS, WindowsPhone8 and Android ICS
That example tries to explain how to add advertising to your xamarin.forms project. The project needs Xamarin.Forms 1.2.2.6243 In the case of Android, the project needs a component of google play service for the version of android. And the version of windows phone needs a adMobs library https://developers.google.com/mobile-ads-sdk/download#downloadios