I taught my nephew the basics of roleplaying in 5 minutes. Here's how it goes.
"You're a prisoner in the top room of a tower. You were brought here by soldiers of the evil Baron Zamox because you, as a knight, could pose a threat to Zamox's claim to power now that the King is away. Your room has a small window, a bed and a privvy chamber. A table nearby holds what remains of your last meal, and a servant should be getting it soon.
What do you do?"
Whenever chance matters, toss a coin 3 times. Easy tasks take only one heads. Hard tasks take two and impossible tasts take 3.
That introduces the person to the basic principle of pretending to be a character, the limitless possibilities of action, and to the element of chance inherent in the game.