How options actually work on binance?

So, often when shopping for bitcoin I arrange buying orders at specific prices. I was speaking about this with a good friend who buys shares using options, and he stated:

You would sell puts at the strike you needed to buy, if the worth is on the cash, you purchase 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 since it was out of the cash the the contract expired I only stored the premium, what occurs if the contract expires on the cash?