From the introduction:
We might as well give you your second shudder here at the start. This booklet really is the second volume of the Game Masters Guide. The first volume is called the Players Guide, but game masters need to know its contents almost as well as players do. This volume picks up where the Players Guide left off. Some of the time it will expand upon themes in the Players Guide that players shouldn't know. Some of the time it will tell you how to make the beginnings in the Players Guide into a finished campaign that succeeds. This volume also will tell you things that you need to do your job that aren't necessarily of importance to your players. But as of this paragraph, you and we both need to assume that you're familiar with the contents of the Players Guide.