In order to watch your parents Cable service, you would have to hook the Slingbox 500 up to a Set Top Box in their home where the service is. The Slingbox will stay there connected to the Set Top Box (cable box). You will need to complete the set up at the Slingbox location, and after that you can watch it at your new place with a computer, mobile device, or connected device.
Hope this helps!
Sling Media Technical Support