A page-post story is a form of sponsored story, Facebook’s social ads, where you highlight a post on a page.
In a normal situation when you make a post, it only appears in fans’ news feeds. But since the news feed is constantly updated, the post will get pushed down rather quickly and there’s a great risk that your fans will miss it.
If you create a page-post story, the post will appear in the right-hand sidebar and the chance of your fans seeing it and clicking on it increases a lot.
The biggest advantage, however, comes when you tie a page-like story to the post. In doing so, you open the door to a large number of non-fans.
Say that you make a post on your fan page and tie a page-like story to it. The post now gets a high visibility and fans click on and like the post.
This “like” will then show in their friends’ feeds – even people who have not yet become fans – and remember that an average Facebook user has 130 friends. It highlights the activity on your page and you may attract new visitors and broaden your fan base. In fact, seeing what friends like is the most effective way to advertise a page and raise brand awareness.
In the actual ad – the page-like sponsored story – you will see how many like it and how many comments it has.
For more information around this and other ways to effectively create ads, read about all advertising methods on Facebook.