Welcome to Android Central! Go to Settings/About Phone, and tap on Android Version rapidly multiple times. After about the 5th or 6th tap, you'll see the Jellybean appear. Hold that Jellybean down for a few seconds, and the beanflinger Daydream scene will appear, and it will now be available to use as a Daydream.
Here's the article discussing it: Unlock the hidden 'BeanFlinger' daydream in Android 4.2 | Android Central
The only problem is I don't know how to save the daydream. When I press the settings soft key nothing happens.
What do you mean by saving the daydream? Once you've revealed the beanflinger, it should now be listed as one of the available Daydreams to use under Settings/Display/Daydream.