Short Selling

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In a short sale, the short seller sells stock shares they don’t own. First, short sellers borrow stock shares from a brokerage firm. They then sell those borrowed shares at the current market price and receive the income into their account. Later, the short seller must decide to close out the short sale by purchasing back the exact number of shares sold to return the borrowed shares to the lender. Short sellers hope that the stock price drops to purchase the stock back at a lower price and profit the difference.

If the price of the stock rises and the short seller buys the shares back at a higher price, they lose money on the trade. When the price of the stock rises, short sellers may hold out in the hopes that it will decrease; since short sellers must eventually repay the broker, they risk losing more money. When the share price increases, it's possible that the broker might issue a margin call, requiring the short seller to put even more money into the brokerage account or close out the trade by repurchasing the stock at the current higher price.

Source: https://www.masterclass.com/articles/short-selling-explained#how-short-…

Borrow their shares (brokerage handles this for you when you want to short)

Sell them at the spot value.

Wait.

Stock price drops. You buy those shares back at the lower value.

And you have now made the spread of when you sold and bought them back for cheaper.