You set up a free account in Prismatic and start to select topics that interest you. You like or dislike them, comment on stories -- something the above-mentioned news apps don't allow -- and you can discuss what you find with other Prismatic users or friends. You can also share on Twitter and Facebook.
The Prisimatic developers say they can find more unique and relevant things for you to look at, and I agree. The app isn't burdened with a lot of the noise that appears in Facebook and Twitter. Content choices are broader than some social apps, because it goes beyond friend recommendations. It scours the web for interesting material. In that way, it is like Zite or Flipboard, but the integration of direct social interaction can make for a more powerful experience.