How options actually work on binance?

So, often when buying bitcoin I arrange buying orders at particular costs. I used to be talking about this with a good friend who buys stocks using choices, and he stated:

You might sell places at the strike you needed to purchase, if the worth is on the money, you buy the asset at the worth you needed, if its out of the cash you get the premium.

Wich is cheap, I did a check with a small sum of money and bought a put, but because it was out of the cash the the contract expired I solely stored the premium, what happens if the contract expires on the cash?