Trading is an index contract. Closing a position is selling the contract. Opening a position starts with the contract. When the contract expires, it will be automatically transferred to next month's contract. If you haven't heard of delivery, where can you get the real thing? The stock index is used to hedge the risk of stock speculators. If you think the stock is going to fall, short it on the stock index. If you fall, you make a profit, and the stock loses, offsetting each other, just like the stock market crash two days ago.

After P.S. closes its position, either you make money or your opponent makes money.