Not only futures can be short, but also Hong Kong stocks can be short, that is, they can be sold by borrowing shares and then repurchased at a low price. Of course, if you borrow a stock to sell, the stock goes up and you lose money. Borrow it from who? Borrow from your brokerage firm, which has its own stock chips. In fact, A shares can also be short, but it is still being piloted by a limited number of brokers and has not yet been rolled out.

As for the index, you can roughly judge your financial knowledge level by the questions you ask, so if you want to explain the index professionally, you may not understand it. You can understand the index as the average price of most stocks. The index has gone up, which proves that most stocks are going up.