A bitcoin exchange operates somewhat similarly to online stock trading brokers, where customers deposit their fiat currency (or bitcoins) to carry out trades. However, not all bitcoin exchanges offer such services. Some exchanges are more like wallets and thus provide limited trading options or storage of currency (both digital and fiat) for trading. The bigger and more elaborate exchanges offer trades between different cryptocurrencies, as well as between digital and fiat currencies. The number of currencies supported by an exchange varies from one exchange to another. (For more, see: Why Is Bitcoin’s Value So Volatile.)
Making money arbitraging bitcoin futures can be extremely simple. Futures contracts typically trade at a premium, and all you have to do, starting with USD, is buy bitcoin at Spot price and sell futures of the same amount at premium price. Then just wait until expiration to make your arb profit in bitcoin (which you can then put in USD). Whether it's a weekly, monthly, quarterly, or any futures contract, as long as it's in a premium, you lock in the sale price and earn the arbitrage profit.