Scan the QR Code on the postcard with your phone (next to the stamp).
Visit the link and install the Adobe Aero application that pops up (usually at the bottom of your phone's screen).
Look at the cat portrait on the other image (the other side of post card).
Make sure your sound is on, then pet the kitty by touching his face on your phone screen (just like he asked in the postcard).
Try moving around the image while looking at him as well. His eyes will follow you.
(Unfortunately not everyone's phone will run the application properly, especially older models. I do apologize if that's the case. I am limited by the technology. You can troubleshoot if you like by visiting Adobe's website for the Aero software.)