Traditionally futures contracts have a settlement date, meaning, when you buy a future with a given settlement date, you are agreeing to buy the underlying product on the day that the contract settles. For example, if you want to lock in the purchase of oil, you may buy a futures contract with for some months in the future because you're concerned that the price of oil will increase before then. This works in both directions, allowing sellers to lock in a price, for example a farmer wanting to lock in a price for their wheat. Depending on what the market predicts as the future price for the underlying, the futures contracts may trade at a premium or a discount compared to the underlying spot price. As the contract moves closer to the expiration date, the contract will trader closer and closer to the underlying spot price, before finally converging at settlement.