The answer to the supplementary question is,

You must be clear that futures is a contract (purchase and sale contract) sale, not a real commodity sale.

The deposit is equivalent to the down payment, liquidated damages and so on.

The contract can be signed at will, provided that there is an opponent (that is, if you want to buy, someone must want to sell, and if you want to sell, someone must want to buy).

In this way, both parties can open positions in futures, and this position is the number of contracts (contract quantity).

On the delivery date, traders who have not opened their positions must fulfill the contract, buyers must go to the exchange warehouse to pull the goods, and the selling price must be sent to the warehouse. If you don't do this, the deposit will be confiscated and the exchange will sue you.

And near the delivery date, the margin ratio will be raised very high, and the breach of contract is not worth it.