Just load the app and point the camera at an of the cover of Soonish. Please note: You do not need to buy anything to use the app. The app is free, and it can be used with any image of the cover, whether digital or physical. You can find one at http://smbc-comics.com/soonish/app/.
When you point the camera at the image, a space elevator will appear, which you can look at from any angle. By moving the camera or the book, you can look around. Take care to notice the tiny cable car running up and down!