Futures and spot are completely different. Spot is actually a tradable commodity. Futures are mainly not commodities, but standardized tradable contracts with some bulk 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 gold, crude oil and agricultural products) or financial instruments.
Short selling, also called "short selling", is symmetrical. Investors predict that the stock price will rise, but their own funds are limited, so they can't buy a lot of stocks, so they pay part of the deposit first, raise money from the bank through brokers to buy stocks, and then sell them when the stock price rises to a certain price, so as to obtain the difference income.