Allowing Users to Post on Your App

I'm trying to make an Android app that would allow users to submit stories. And when they submit it, then all other users who have the app should be able to view the new stories. And so with each new story that's submitted, all users should be able to see an updated list of stories. But I'm not really sure how to push these changes to all users once someone submits a story.
I guess as a reference, this would be most similar to apps like FML or even facebook in the sense that someone posts something and everyone should be able to see it.

Any help would be appreciated! And I'm willing to clarify anything!