1. Index: It means that you are trading stock index futures.

2. Short selling: It means that you expect the stock index to fall, so you do short selling and open positions.

If the index falls, it can be leveled again by buying short.

Warehouse, so as to obtain the difference profit.

3. Option: It's hard to understand in definition. I'll give it to you when it's done.

Buy futures and buy an insurance. You must pay a certain amount of insurance.

Fee, if your expected price trend is correct, you can ask.

Perform the contract, buy the short position at the original price, and then close the position to understand;

If the expectation is wrong, what you have to do is not to perform the contract, and your loss.

It's just insurance