This initializes the member WebView with the one from the Activity layout and enables JavaScript for the WebView with JavaScriptEnabled = true (see the Call C# from JavaScript recipe for information about how to call C# functions from JavaScript). Finally, an initial web page is loaded with LoadUrl(String).
Because this application needs access to the Internet, you need to add the appropriate permissions to the Android manifest file. Bring up your project's properties with Project -> HelloWebView Properties. This can be done is Xamarin Studio by right clicking on the project and going to Options -> Android Application. Since there is no default manifest file, click the link to add one: