Buy more means that investors buy a futures contract, hoping to sell it at a higher price at some time in the future, thus making a profit. Specifically, buyers think that the price of futures contracts will rise, so they buy now and sell at a higher price in the future, thus making a profit. For example, if an investor thinks that the price of a commodity will rise in the future, he/she can choose to buy more futures contracts for that commodity.
Short selling refers to investors selling a futures contract, hoping to buy it back at a lower price at some time in the future, thus making a profit. Specifically, short sellers think that the price of futures contracts will fall, so they sell now and buy them back at a lower price in the future, thus making a profit. For example, if an investor thinks that the price of a commodity will fall in the future, he/she can choose to short the futures contract of the commodity.
It should be noted that short selling is a risky operation, because in futures trading, prices can keep rising, and short sellers need to buy back at a lower price in the future, so they may face unlimited risks. In addition, in futures trading, the profit and loss of long and short operations are related to the price at the time of contract delivery, and investors need to make adequate risk assessment and trading plans before trading.