Press green flag. Wait as long as you want. Press space if your on a computer to view whatever was created. From there you can just screen shot it and set it to your background or whatever you want to do with it. If you're on a mobile device, stop the program, hide the cat, and then screenshot.
I got bored and decided to through a bunch of blocks together. This was the outcome. I might even come back to this and make it even cooler. If you get a boring design, just wait a little longer and something cool will come up eventually. This is for those of you who actually read these things :P : If you want, you can leave the project running for a while on your desk or somewhere else because it is actually quite mesmerizing to watch :D.