I want to run the Xamarin project and did all the updates. When I run the project I get the following error
The type or namespace name 'Windows' could not be found (are you missing a using directive or an assembly reference?)
for the lines
using Windows.Storage;
using Windows.ApplicationModel.ExtendedExecution;
That's because you're missing these .dll
The recommended steps to get access to UWP APIs are listed in the dedicated blog post on Windows Blog. Basically you can take two approaches: add the references to UWP dlls and winmd files manually or use the UwpDesktop NuGet package that will take care of this for you automatically.
For more details, you can check: How do I get access to Windows.Storage namespace?