All display real-estate is won through auctions, and Facebook has two major types of ads - Premium and Self-serve. Premium ads offer 100% share of voice, while self serves are mostly have around 25-33% share of voice. While most creatives have standard information, comprising of a header, an image, some info, maybe an action spec (eg. your friend likes this) and appear only on the right hand side, sponsored stories will appear in your feed, and will have a larger creative.