With Fan Accelerator, people who write a review about a product outside of Facebook can check a box to also become a fan on Facebook.

FORBES: Buying On Facebook Is Hot As PowerReviews Accelerates Fans

The Sponsored Story could come from an advertiser itself or it could be some product review you write which a company then sponsors.

FORBES: Why The Higher Click-Through Rates for Mobile Ads Which Facebook Touts Mean Nothing