If you want to play around with the supercool new Windows.UI.Composition API in Windows Universal apps, you'll need to keep in mind that the API is still in preview. The API is subject to change and a final version is expected to be available later this year. This however should not stop you from giving it a spin.
Unfortunately, when creating a new Universal Windows app and accessing the Windows.UI.Composition classes, you might run into the following error;
An exception of type 'System.UnauthorizedAccessException' occurred in xxx.exe but was not handled in user code Additional information: Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))
Access to the preview Composition API is by default restricted, you'll need to add a capability to your appxmanifest. Here's how;
For a full sample Package.appxmanifest see this package.appxmanifest on GitHub