The "call to action" button is designed to bring a business’s most important objective to the forefront of its Facebook presence, call to action buttons link to any destination on or off Facebook that aligns with a business’s goals.With the feature, Page admins can choose from a group of seven calls-to-action, which include “Shop Now,” “Sign Up,” “Book Now,” “Contact Us,” “Use App,” Play Game” and “Watch Video.”

With this button you can direct users to shop your store, register for an event, sign up for your newsletter, etc. This is a great way to direct traffic to your web site. 

The button is in the lower right corner of the cover photo.