When purchasing put options, you are expecting the price of the underlying security to go down over time (so, you're bearish on the stock). For example, if you are purchasing a put option on the S&P 500 index with a current value of $2,100 per share, you are being bearish about the stock market and are assuming the S&P 500 will decline in value over a given period of time (maybe to sit at $1,700). In this case, because you purchased the put option when the index was at $2,100 per share (assuming the strike price was at or in the money), you would be able to sell the option at that same price (not the new, lower price). This would equal a nice "cha-ching" for you as an investor.

You also can limit your exposure to risk on stock positions you already have. Let’s say you own stock in a company but are worried about short-term volatility wiping out your investment gains. To hedge against losses, you can buy a “put” option that gives you the right to sell a particular number of shares at a predetermined price. If the share price does indeed tank, the option limits your losses, and the gains from selling help offset some of the financial hurt.
However, unless soybeans were priced at $15 per bushel in the market on the expiration date, the farmer had either gotten paid more than the prevailing market price or missed out on higher prices. If soybeans were priced at $13 per bushel at expiry, the farmer's $15 hedge would be $2 per bushel higher than the market price for a gain of $2,000,000. On the other hand, if soybeans were trading at $17 per bushel at expiry, the $15 selling price from the contract means the farmer would have missed out on an additional $2 per bushel profit.
For example, if you believe the share price of a company currently trading for $100 is going to rise to $120 by some future date, you’d buy a call option with a strike price less than $120 (ideally a strike price no higher than $120 minus the cost of the option, so that the option remains profitable at $120). If the stock does indeed rise above the strike price, your option is in the money.
An option is a contract that allows (but doesn't require) an investor to buy or sell an underlying instrument like a security, ETF or even index at a predetermined price over a certain period of time. Buying and selling options is done on the options market, which trades contracts based on securities. Buying an option that allows you to buy shares at a later time is called a "call option," whereas buying an option that allows you to sell shares at a later time is called a "put option." 
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