The introduction begins by touting how great AD&D is, going so far as to claim that it is "superior to any past offerings in the fantasy role playing game field". It also states that the system has been "written and edited in order to make the whole as easily understood as possible". Given that there are still people arguing about the intent of these rules nearly 40 years later, I have to call foul on this one.
It goes on to describe the various races and classes included in the PHB, and the relative balance of each. It's stated outright that fighters and clerics have been strengthened in relation to magic-users; no doubt Gary experienced the difference in raw power between the classes first-hand. His claim that "none of these over-shadow thieves" is a little dubious, but I'll let it slide; while thieves are notably weaker in combat than the other classes, they fill a vital role in other areas of the game. The classes and sub-classes mentioned have all appeared in the game before, but there's a new race made available to PCs for the first time: half-orcs.
Finally it gets around to trying to explain what a fantasy role-playing game actually is, which it does in vague terms. It's a world of imagination created by the Dungeon Master, explored by the players, full of monsters and treasures, etc. A more concrete example of how the game is played would be useful here.
Possibly my favourite part of this intro is the futile urging that players not buy or read the Dungeon Masters Guide. (Not so futile at the time of publication, I suppose, as the DMG wouldn't be available for another two years). I admire the sentiment that certain parts of the game should remain mysterious to the players, but it's ultimately impractical. Inevitably those players will want to run a game themselves, and even those that don't are going to crack the DMG open eventually. Anyone sufficiently dedicated to the game is going to want to learn its inner workings, and there's little anyone can do to stop it.
Here we get a little deeper into what playing AD&D entails. It begins in typically hyperbolic style, describing how the player and his friends act out the roles of their characters, and work together to achieve their goals. Particular attention is given to the idea that AD&D is played over multiple sessions, and that characters start weak but gradually grow in power. The role of the DM in crafting a challenging world is stressed, followed by some of Gary's ideas on what constitutes a good player: have an objective, cooperate with your fellow players, know when not to combat monsters, and don't be a dick to the DM. Sound advice.
It finishes up by noting that a character's stats must be accurately recorded (which you might like to do on an official character record published by TSR!). Still no example of how the game is played.
There are some named PCs that I will use in my campaign: Falstaff the fighter, Angore the cleric, and Filmar, mistress of magic. (I won't dignify the last with an exclamation point, as Gary did.)
CREATING THE PLAYER CHARACTER
The basics of character creation are outlined here: roll your abilities using the dice, choose a race and class, pick your alignment and name your character. Some other steps are briefly described (languages, money, hit points), but that's the general gist of it.
It's stated outright that all characters begin at 1st level. I've never tried this in practice; being basically soft-hearted, I allow PCs to begin at around the same level as the existing party. I need to try it some time, if only to test the survivability of low-level characters adventuring with a higher-level party, and how long it takes them to catch up in experience.
The use of the term "level" is outlined, and it becomes apparent just how widespread it is in the game: it's used to denote character power, the strength of monsters, the power of spells, and the depth of a particular dungeon tier. Gary mentions that he was contemplating some new terms: rank instead of character level, power instead of spell level, and order instead of monster level. I feel like that would ultimately have caused more confusion than it solved. The use of level as a catch-all works well as a way of describing how strong or dangerous something is, and Gary made the right call in keeping it.