The way you asked this question, it shows that you don't understand trading that much. I'm not even sure if you ar  conversant with spot trading talk more of the futures you are asking about.

There is different between a margin trading and futures trading. In a Margin trading, it's always assume that you have limited amount of money to trade, so what the exchange does is that they borrow you fund to add to your available funds to trade and buy the coin you want to trade. However, the available balance will be held as collateral so that if the funds lend to you is about to hit liquidation, it will be automatically force close and your availablr balance is what will be used to settle the funds you borrow.

Futures on the other hand is using your available balance to bet on the price of bitcoin and there must be another trader that must be ready to bet with you to in opposite and once that order is settled with the leverage selected. It will be in the favour of the trader that the market move in the direction.