AndroidManifest is a powerful file in the Android platform that allows you to describe the functionality and requirements of your application to Android. However, working with it is not easy. Xamarin android helps to minimize this difficulty by allowing you to add custom attributes to your classes, which will then be used to automatically generate the manifest for you. Our goal is that 99% of our users should never need to manually modify AndroidManifest.xml.
AndroidManifest.xml is generated as part of the build process, and the XML found within Properties/AndroidManifest.xml is merged with XML that is generated from custom attributes. The resulting merged AndroidManifest.xml resides in the objsubdirectory; for example, it resides at obj/Debug/android/AndroidManifest.xml for Debug builds. The merging process is trivial: it uses custom attributes within the code to generate XML elements, and inserts those elements into AndroidManifest.xml.