Xamarin
Xamarin Tutorial for Absolute Beginners https://www.youtube.com/watch?v=6MQXkUfIn9M
Visual Studio and Xamarin : https://www.visualstudio.com/xamarin/
10 minute guide to building mobile apps in C# : https://www.xamarin.com/getting-started/android
Installing Xamarin.Android on Windows : https://developer.xamarin.com/guides/android/getting_started/installation/windows/