Short selling is a kind of trading behavior, which is to sell and open a position before buying and closing a position. The price difference is your profit. For example, soybeans are now 4500 yuan per ton, and it is expected to fall in the future. You sell the open soybean contract at 4500 yuan, and then buy the open soybean contract when the price drops to 4400 yuan. So you earn 100 yuan per ton.