My memory is rusty but I'll try to answer. Firstly, I'm not sure whether you meant sell or buy naked put. Because a bearish person will buy puts not sell puts. A bullish person will sell puts not buy puts.
When you write a put, you are selling the right (not obligation) to sell the underlying asset at a price. This 'right' expires on a certain date.
American options means it can be exercised before and on the expiration date. European options means it can only be exercised on the expiration date.
Let's say stock A price is $100 today. You speculate that the share is undervalued and will rise. So you write a put with strike price $100 thinking the share price will rise above $100 by the expiration date and collect a $5 premium.
If the price falls below $100 say $70 and the buyer of your put option exercises it, they sell the share to you at $100. Technically, you don't want this stupid share that you bought at $100 when the market value is only $70. So, your loss is $100-$70=$30. However, you gain the $5 premium earlier. Hence, net loss is $25 ($30-$5).
Your max gain if the option expires worthless is +$5.
Your max loss is -$95 ($100-$5). Assuming the share falls to $0 but it's unlikely.
Tldr; it's a gamble.
I believe there are several ways to protect yourself while shorting the market. One is called bear spread strategy.
Thanks. I believe danmooncake was talking about selling naked Puts (refer to his earlier posts) . And yes, I am talking about that risk of $25 net loss, if the market really tanks.