This is how i will explain this to my wife:

Crypto is another form of currency that we can use like normal money to buy some stuff. There are not much shops who accept this form of money right now but there will be a lot in the future.
Just like all the countries have their own money similarly this is money for internet. This money can be used beyond country boundaries and this currency is not printed on paper. It's like using credit/debit card to pay for goods and services.

Hope i did not make it much complex.