How do you explain crypto to 10 year old?

[King Belieal]

I met a lady that came to ask me some questions about the entire crypto thing and how it works. She told me to explain crypto to her as I am explaining it to a 10 year old child.

I really didn't know how to do that. I am sure she didn't understand my explanation. How do you explain crypto to a 10 year old child? By that, I mean simple, basic explanation.