A Bitcoin futures contract is exactly what you would expect from the example above, replacing pork bellies with Bitcoin. It is a contract that enables you to buy Bitcoin at a predetermined price at a specific point in the future. For example, if today’s Bitcoin price is 8,000 USD per BTC and you expect it to rise to 10,000 USD per BTC in 4 weeks, then entering a contract which allows you to buy Bitcoin at 9,000 USD in 4 weeks is highly attractive.
In this guide we don't want to deal with social loss risk, so use the FCA-regulated, London-based bitcoin derivatives exchange CryptoFacilities. They offer contracts with 2% margin requirement (50x leverage) as well as a 15% margin requirement (6.5x leverage). They are 100% bitcoin based, but they don't accept US customers. Sign up here to get started: