Futures contracts, when they trade on regulated futures exchanges, obligate you to buy or sell a specified quantity of the underlying product for a specific price on a specific date. The underlying product could be a commodity, stock index, security, or currency. Because all the terms of a listed futures contract are structured by the exchange, you can offset your contract and get out of your obligation by buying or selling an opposing contract before the settlement date.
Futures contracts provide some investors, called hedgers, a measure of protection from price volatility on the open market. For example, wine manufacturers are protected when a bad crop pushes grape prices up on the spot market if they hold a futures contract to buy the grapes at a lower price. Grape growers are also protected if prices drop dramatically - if, for example, there's a surplus caused by a bumper crop - provided they have a contract to sell at a higher price.
Unlike hedgers, speculators use futures contracts to seek profits on price changes. For example, speculators can make (or lose) money, no matter what happens to the grapes, depending on what they paid for the futures contract and what they must pay to offset it.