The essence of futures is to sign long-term contracts with others to buy and sell commodities (or stock indexes, foreign exchange, interest rates) in order to achieve the purpose of maintaining value or making money.
If you think the futures price will go up, go long (buy and open positions), go up (sell) and close positions, and earn: price difference = close positions-open positions.
If you think the futures price will fall, short (sell the position), fall (buy) and close the position, and earn: price difference = opening price-closing price.