This opens with exactly the same overview of the background and current state of the setting as is to be found in the Player's Guide, along with the note that it designed to be used with The Basic Fantasy Role-playing Game ruleset, but that any OSR rules will do. There's also mention that this is for the Game Master and that although they will need to consult the Player's Guide occasionally, this will be their main reference.
The first topic to be explored is encounters, divided up into dungeon, wilderness and urban ones. The use of random tables is encouraged, which will of course be different depending on which environment you are in... indeed, you may well find it useful to construct several for different places in each environment type, as well as according to party level, time of day (at least, when outside) and the like. There are plenty here to be going on with, complete with explanations of what each list entry signifies. From this, we move on to how to create a group of NPCs, including adventuring parties, brigands/bandits, pirates and all manner of undesirables as well as groups of merchants, nobles and pilgrims. Some might be friendly, but that's rather brushed aside as "making things too easy for the players"! This includes allocation of magic items and using non-humans.
Next comes a section entitled Dealing with Players. This begins with how to deal with players who don't like the statistics they've rolled for their character then moves on to the acquisition of spells including how clerics may be limited according to the deity they revere and how magic-users gain their spells. Also touched upon is what happens if a character uses armour or weapons that are 'prohibited' for them. There's a fair bit of discussion of advancement and how to deal with character death as well. We then move on to magical research with plenty on creating new spells or magic items as well as enchanting weapons.
This is followed by advice on how to create adventures, beginning with that classic, the dungeon adventure. The first thing to decide is why they party wants to go into a dungeon in the first place. (I remember asking that the very first game of D&D I played... the rest of the party had no real answer for me - might have helped if they'd read this!) Once you've decided why they are going there, decide where 'there' is, decide what monsters to use and draw a map. Then 'stock' the dungeon - assigning contents (including monsters) to each room, not forgetting puzzles and traps as well as monsters to kill and treasures to loot. Some sample traps are provided. Wilderness adventures then get a similar treatment, with an area map rather than a detailed floor plan, and this leads neatly into strongholds, as those might be found in the wilderness. This discussion includes building costs (maybe your party wants to construct a base) and a note that a stronghold might have a dungeon underneath it, as well as a few notes on laying siege to the place. In some ways it's all very basic and obvious, but if you are new to GMing could prove invaluable.
Next up, Monsters. There are notes on how they are described, and then a selection of them (including plenty of dragons!) ready for you to use. Some are sentient, like gnomes or giants, others are of animal intelligence or lower, like the gelatinous cube. Of course some, like ghosts, are undead, and lycanthropy is also covered.
Monsters dealt with, the discussion moves on Treasure. Plenty of charts to help you determine what there is to loot... and a section on using magic items once you have laid hands on them. Lists of magic armour, magic weapons, potions, scrolls, rings and other items follow, covering what they do and what benefits (or otherwise, if they are cursed) they confer.
Finally, there are thumbnail sketches of various kingdoms and other lands within the setting. I'm crying out for a map here... although this book is well-illustrated I like a map to get oriented! The descriptions are good, though, bringing each polity into vivid life.
This work provides a wealth of basic material to set you off on a path to running effective adventures. Whilst much work remains to be done, the scaffolding is here to aid you in developing places and adventures to happen in them. Have fun!