I wouldn't tell much but will use simple words such as its a digital currency that can be use as payment for goods and services online whereas the seller is willing to receive bitcoin.
It has an unstable value that the market gives depending on the demand and supply of it. And if that isn't enough its better for him/her to watch tutorials that's explanation bitcoin with some visual graphics.
Maybe additives to this dude,let them see how it workds in our life being in cryptocurrency,so by that they will have a basis to look at,and my attract them to enter this community,from this maybbe they will be the one to seek knowledge about all the fundamentals of crypto world