How can this basic concept become a game?
Making some kind of prototype to test different aspects of the game (I suppose this is the point of all of this). There’s lots of ways to flesh out a basic concept, but I think the main way is just trying different things and adding what works, and isolating different variables when testing.
What is the theming/style of the game outside of the mechanics?
Thinking about this is important, figuring out the world that the game is in can be just as important as the mechanics themselves. You can have good lyrics and bad music, and good music and bad lyrics, but they have to work together to make a really good song. This is how the game feels like something.
How can we make it easy to explain?
I think using examples is good, but also just making the gameplay easy. There should be a pretty clear why, like “you’re trying to solve a mystery,” or “you’re trying to get to know each other,” and I think leading with that will provide ample instruction not only for people to understand how to play the game, but also for us to design it.