Traditional concept: futures and spot are completely different. Spot is actually a tradable commodity. Futures are mainly not commodities, but standardized tradable contracts with certain mass products such as cotton, soybeans and oil and financial assets such as stocks and bonds as the targets. Therefore, the subject matter can be commodities (such as financial instruments, crude oil, agricultural products) or financial instruments.
Vernacular explanation: futures are due for delivery. For example, I negotiated the price with Li Lei, and Li Lei gave me the goods a month later.
Subject: This is what we want to trade. I want copper, copper is the theme, I want soybeans, soybeans are the theme. Just a different name.
Standardized contract: I negotiated the price with Li Lei, and he gave me the goods a month later, but I'm worried that if he doesn't sell it to me then, I'll blow it up. We have to discuss a way, that is, we sign a contract. I am relieved that the contract is here. Only in the futures market, we don't have to make this contract, this contract is made by the exchange. The person in charge of the market booked a contract for us, which is a standardized contract. It is equivalent to the enactment of laws (only later revised) to regulate people's behavior. The same is true of standardized contracts.
Margin: I signed a contract with Li Lei, and Li Lei is worried about what I will do if I don't want his goods. Li Lei came to see me again. We discussed it, and I will pay you a deposit, but I am afraid that Li Lei will run away with the deposit. That won't do. We need someone we can trust as a middleman to supervise both of us. So we found Han Meimei. I gave the deposit to Han Meimei, and Han Meimei supervised me and Li Lei. The money I gave Han Meimei was called a deposit.
Futures trading: I signed a contract with Li Lei, and he will give me his goods in the future, but now my company has reduced production and stopped working. I don't need Li Lei's goods, so what should I do? I'll go to Han Meimei and tell her. Han Meimei said, "I happen to have someone here asking me if I have any goods. Why don't you sell him the contract in your hand and I'll refund your deposit. " I readily agreed. Han Meimei told it to Li Lei again. Li Lei said: "I don't care who I deal with, I only recognize the contract, and I will give the goods to whoever brings the contract." From this perspective, my transaction with my friends in Han Meimei is just a contract in my hand, that is, futures.