How do you think you give your account then? Adding a payment method is where you will receive the amount you exchange from the seller.
You will still need to add a payment method in order for the seller to send the amount you exchange to the payment method that you add in your P2P account without adding it you won't be able to exchange anything from Binance P2P.
You just didn't understand how Binance P2P works but if you already have an account on Binance check it there and I'm sure you will still need to add a payment method where you will receive the money you can add the payment method it could be a bank account or any other payment methods available in your country. You can also try to add the payment method of your friend's bank account but I do not know if it will work because based on my experience on Binance P2P they don't allow me to add other payment method or bank account that doesn't have the same name if what name you registered on Binance you must use an account with the same info or name when adding a payment method.