The first thing someone sees when they log into Facebook is the newsfeed. But not every update of you is syndicated to each of your fans. So the question is how will the post roll in to their newsfeed?
Facebook has an algorithm called EdgeRank where you must score high. It is the algorithm that decides which stories appear in each user's newsfeed. The algorithm hides boring stories, so if your story doesn't score well, no one will see it.
As Facebook Page Marketing is rapidly becoming one of the foremost marketing tools used by the Brands, here is an infographic by Post Rocket for better understanding of EdgeRank.