Futures is a standardized forward contract, as opposed to spot trading, which promises to deliver the goods at a certain time in the future (quality, quantity, trading time, trading places and trading price have been determined in advance). Because it is not a spot transaction, it is either sold or bought. To put it bluntly, you promised something to be provided in the future, not now, so you can sell it first. Even if delivery is required at maturity, you can avoid physical delivery by closing your position.

Stock trading is equivalent to spot trading, and the transaction must be transferred immediately, and the stocks that are not held cannot be sold.

Stocks can also be traded in futures. For example, you have agreed with others to buy or sell a certain number of stocks at a certain price in the future, even if you don't own the stock now.

The above is my own review again, which may not be accurate and is for reference only.