how to use action bar in xamarin android

ActionBar is basically shown on the top of the application. You can use this control to allow the users to perform multiple actions, such as changing the content of the application, starting a new activity etc. There are many functions that an action bar can handle. It can also show the "title" of your current activity, provide the support for menus and other user-interactions.

For more on this, please read the following guide, https://developer.xamarin.com/guides/android/user_interface/actionbar/