Tell them whatever you know in the most simple terms.After that link them to this video:
https://www.youtube.com/watch?v=RZ_3MKomQzYHail this guy aka Jesu stall man(he is the sticky of 4chan/g lol).
This video might make them more curious about cryptos.After this, just give them time.If they aren't lazy ignorant plebs, then they will try to know as much as they can.
Its been 5 years, since I get to know about bitcoins.And I am still learning! Once you enter this chain, you don't stop.
If you want to explain to people who aren't digitally active, then just tell them its a de-centralized currency who's value is determined purely by demand-supply; and other basic things.No need to get into blokchain,mining part.It's too complicated for them to grasp.That's where people get confused and lose their interest.
Good luck!