Futures is to pay money, but it will take some time to get the goods, but the price is fixed and cannot be changed when trading. Spot is the current transaction, with one hand paying and one hand delivering.

Give a simple example:

You go to the market to buy apples, 10 yuan a catty, and you pay 10 yuan to get a catty of apples, which is spot trading.

You bought it, but you didn't. You agreed with the apple seller to buy it tomorrow, 10 yuan a catty. This is a futures transaction.

The difference between crude oil futures and spot crude oil is the same. The agreed price is very strict and cannot be changed.