Just like it sounds, this is a guidebook aimed at players. It’s short–only 64 pages–and includes only material for the corebook.
In other words, there’s nothing in the Player’s Guide that isn’t in the corebook. It’s very useful, because there’s no need to hand a new player a 416-page rulebook to get them started. It has only the material that a player needs to get a feel for the game and the setting, and to create a character.