Exchanging messages is a good metaphor, but maybe too atomical.

I think that describing it as a neverending word game with defined closed set of moves can be a level closer to their understanding, and yet reveal your point.

Word Chain Game is the best example (the one where you have to come up with a word startomg with the last letters of the previous word). Traditionally a spoken game, but can be played on computers, in online multiplayers, ...

Playing Bitcoin is like playing the Spelling Bee PR the Wordle.