Put Option

Put Options are options to sell a stock at a specific price on or before a certain date. In this way, Put options are like insurance policies
If you buy a new car, and then buy auto insurance on the car, you pay a premium and are, hence, protected if the asset is damaged in an accident. If this happens, you can use your policy to regain the insured value of the car. In this way, the put option gains in value as the value of the underlying instrument decreases.

If all goes well and the insurance is not needed, the insurance company keeps your premium in return for taking on the risk.

With a Put Option, you can "insure" a stock by fixing a selling price.
If something happens which causes the stock price to fall, and thus, "damages" your asset, you can exercise your option and sell it at its "insured" price level.

If the price of your stock goes up, and there is no "damage," then you do not need to use the insurance, and, once again, your only cost is the premium.

This is the primary function of listed options, to allow investors ways to manage risk.