Futures exchanges are used to trade commodities. It's when a buyer and supplier agree a price and deal for something in the future. For example a carrot farmer may agree to sell his carrots to Gary in 3 months time when they're finished growing. It's used when the product / commodity isn't ready yet.
It's also used for hedging and other complex financial stuff- but you don't need to know that yet. Commodities and Future contracts are a big part of L5M4 to warn you though. Futures Contract Definition: Types, Mechanics, and Uses in Trading (investopedia.com)