Getting into RPGs is kinda like nothing else. Which is a problem for new players, and an even bigger problem for anyone who tries to explain the concept to a total muggle.

“It’s like theatre combined with a game!” only, not really, because you don’t really have to be theatrical, and no one should judge you on how well you act, if at all.
“It’s like a movie, only you decide where the character goes!” yes, but, you don’t simply control a character’s actions, you can also enjoy playing her personality and inner conflicts, and also, you have a huge influence on the rest of the fiction (in some modern systems you can invent most of the world during play).
“It’s like an improv show, and you play through a story as you make it up!” But you don’t really have to work hard on the imaginative part (improv shows are hard work), and there’s also an actual game, with rules and various win conditions, which is a huge appeal for a lot of players, and yet you didn’t even mention it.

I’ve been in the Explaining RPG to Muggles business for about 15 years now, it’s been both my job and my hobby, and I’m yet to find a perfect solution, but I think it’s because there isn’t one. RPGs are a complex concept, and as any marketing person will probably tell you, such a concept should be dissected into several clear and distinct ideas; take the one best suitable for the target audience, and use it to capture their attention – add the other ideas after they’re already hooked enough to care.

Are you talking to a curious kid with a Star Wars shirt? Say it’s like a movie in which you can control the character’s decisions. It’s not a full description, but it’s enough for now; after you get him to the table, tell him all about narrative power and getting into a character’s inner world. Is this woman interested in the concept of “being someone else for a few hours”? Start there, and only later add some explanation about the role of dice in the game, based on that perspective – the rules make sure this fictional character’s life will be interesting.

 

Read this story arc from the beginning: Gathering the Party