See the iOS integration instructions for information on how to integrate the News Feed into your Xamarin iOS app. Furthermore, you can look at the [sample application] implementation samples.
Of all the implementation options, the quickest to implement is the Modal, which can be added by doing
1 2 3 // C# ABKFeedViewControllerModalContext m = new ABKFeedViewControllerModalContext (); this.PresentViewController (m, true, null);
in your ViewController.