Here's something I came up with recently - a written version of the more-or-less standard verbal intro I give to people interested in playing D&D with me. This spiel takes about 2-3 minutes and I think it's a pretty good encapsulation of the core concepts and activities of the game as I like to play it:
The game is set in a fantasy world that's pretty much like Middle Earth plus a lot of elements from mythology and fairy tales - so there are vampires and medusas and genies and unicorns and stuff running around with the orcs and elves and dragons. Magic works and some types of characters can cast spells - magic-user characters learn them from studying books; clerics have them granted by the gods. Fighters and thieves don't cast spells but even they can use magical items like potions and rings and flying carpets and invisibility cloaks and such if they find them.
You're going to start out as a beginning adventurer, so at first your goal is going to be to try to gather treasure - gold and jewels and magic items - because that's how you'll become more powerful and able to face bigger challenges (and eventually pursue other goals). Most treasure is guarded either by monsters, which you can fight or try to trick, or by traps, which you can avoid or try to disarm. There will also be puzzles and riddles and such that you'll need to solve, and things and people that you can talk to - some of which might be able to help you, but others will try to trick you.
It's a dangerous world, so especially as a beginning adventurer there's a good chance you're going to end up dead, but if you do survive and manage to get some treasure, the longer you live the more powerful you'll become and the better your odds of survival will be. But if you don't, that's okay too, you just start over with another character, and hopefully that one will have better luck and you'll learn from any mistakes you made. It's no big deal if you lose a character or two, especially at the beginning.
The way the game works is that you imagine yourself with the capabilities of your character (fighting skill, spells, gear, and so on) in the situations I describe, and then tell me what you want to do. I tell you what happens, and a lot of times I'll have you roll dice to see if you succeed. It'll probably seem a little overwhelming at first but eventually you'll get the hang of it. Don't get hung up on all of the rules and numbers - I'll take care of all that stuff behind the scenes. Just try to picture yourself in the scene and then do whatever it is that you would do if you were there. And don't be afraid to ask questions if you're confused about anything I've described or want more details about anything. The game moves fast so you'll need to make decisions and say what you're doing quickly when I call on you, but you'll usually have time to ask some quick questions, and I'll go a little easy on you at first while you're getting used to it.
It's important to pay attention to the descriptions I give, because a lot of the time there will be details that are important - clues that will help you survive or find hidden treasures. And sometimes there will be things that I didn't think of that you can use to your advantage, which is why it's important to try to imagine the scenes as vividly as you can. That's one of the best parts of the game - that it's open-ended and grows, so the more you imagine the more real it becomes. I've set up some challenges and environments, but there's no script or single correct path. As you play, the game becomes what you make it, and eventually you'll end up setting your own goals and directing way more of what happens than I do.
The game's going to start with you arriving in a town, where the first things you're going to want to do are talk to people to find out where the adventures are - where you can go to look for treasure - and buy all the gear you're going to need (and you should probably find a place where you can sleep between adventures while you're at it). Doing all of that will help you get an idea of what the world's like, and will also ease you into the idea of thinking and acting and speaking like your character, so that hopefully by the time the actual adventure starts and your character's life is on the line you'll already be pretty comfortable with how it all works.
So what do you say we get started rolling up your character?