Let's say that the person doesn't know anything about bitcoin and much less about money. Well, there's no other option, he has to learn in a simple way what money is. How would you do it? By giving him a brief history of money from barter to fiat money. Up to this point he should already understand that money is a means of exchange, to obtain goods and pay for services. So he already knows what money is, but why bitcoin and not the dirty fiat? There we would talk about how banks work, how they multiply money out of nothing (fractional reserve) and that this leads to more inflation compared to bitcoin which has a fixed emission. The truth is that there is a lot to start with, but knowing what money is is important.