From the post:
As the Pathfinder Playtest begins, Game Masters will need to quickly get up to speed with the new rules. The Game Mastering chapter of the Pathfinder Playtest Rulebook is here to help you out! It covers the responsibilities of a GM, gives advice on running sessions, and teaches you how to adjudicate the rules of the game. Because this is a playtest, there aren't details about creating your own campaign or adventures, but rest assured, this information will appear in the Pathfinder Second Edition rulebook!