How-to: enable OS X built-in VNC Server – Docs - Flow Swiss

Connect to your Xcloud instance and login:

- If you have a Mac device, you can use OS X’s built-in Screen Sharing, Apple Remote Desktop or any available Mac VNC App by supplying your public Xcloud IP address, user name, and password.

- If you don't have a Mac device, you can use the HTML5 Console within the Customer Portal to connect to your instance.
Open System Preferences > Sharing > Remote Management > Computer Settings
Enable "VNC viewers may control screen with password" and enter your desired password. (Password: 8 characters max.)
Confirm changes with OK
You are able now to connect with any VNC Client using your password configured in step 3.