The four actions that are easiest to mix up in options trading are: Buy to Open, Buy to Close, Sell to Open, and Sell to Close. I’ve seen plenty of beginners trip up here, so today I’ll lay it out clearly from a trader’s perspective.

First, let’s talk about the basics. An option is essentially a contract that gives you the right (not the obligation) to buy or sell an asset at a specific price on a specific date. The contract has two sides: one is the holder (buyer), and the other is the seller (the option seller). The buyer pays money to buy the rights, while the seller receives the money and assumes the obligations. If the buyer chooses to exercise the right, the seller must perform.

There are two types of options: call options and put options. A call option gives you the right to buy—you’re betting that the price will rise. A put option gives you the right to sell—you’re betting that the price will fall. For example, suppose XYZ company’s stock is currently $15. You buy a call option with a strike price of $15 and an expiration date of August 1. If at expiration the stock price rises to $20, you can buy at $15 and make a $5 profit. Conversely, if you buy a put option and the stock drops to $10, you can sell at $15 and also make a $5 profit.

Now let’s cover the trading actions. Buy to Open means you newly buy an options contract, becoming the holder. This is the entry action—you pay the premium to the seller and gain all the rights associated with that contract. Buying call options means you’re bullish; buying put options means you’re bearish. This action sends a signal to the market: you have a clear expectation about a specific direction.

But trading isn’t just about buying. Many people choose Sell to Open, which means writing a contract and selling it to others. You collect the premium, but at the same time you take on the obligation. For example, you sell a call option to Martha with a strike price of $50 and an expiration date of August 1. If Martha exercises, you must sell to her at $50. If the stock price is $60 at that time, you lose $10. This is the seller’s risk.

So how do you stop the loss? That’s where Buy to Close comes in. You go into the market and buy an identical contract to offset the one you sold. If the call option you sold is owed $1 to the market, then the call option you buy earns $1 from the market. The two contracts offset each other, and your position becomes zero. Of course, you have to pay a premium to buy this new contract, and this cost is usually higher than the premium you received when you first sold—but you’ve successfully exited.

Correspondingly, Sell to Close means that you originally held a call or put option, and now you sell an opposite contract to close the position. For example, if you bought a call option, you now sell the same call option to lock in gains or limit losses.

Why does this mechanism work? You can thank the Clearing House. Each major market has a third-party institution like this: it aggregates all trades and performs settlement. In the options market, you don’t trade directly with the seller—you trade through the Clearing House. The contracts you buy come from the Clearing House, and the contracts you sell are also sold to the Clearing House. If you exercise, you receive money from the Clearing House; if you owe money, you pay the Clearing House. As a result, all receivables and payables are settled relative to the entire market. That’s why Buy to Close can perfectly offset your position—the market automatically clears to ensure your income and expenses balance.

To summarize: Buy to Open is an entry action—you establish a new position; Buy to Close is an exit action—you eliminate your previously sold position by buying the opposite contract. Similarly, Sell to Open enters the market by selling a new contract, while Sell to Close closes the position you hold by selling the opposite contract. Together, these four actions allow traders to enter and exit the market flexibly.

Options trading really is complex and involves things like taxes and risk management. If you plan to get into this field, it’s best to first understand these basic operations, and then consider your own strategy. Remember, options trading can make you a lot of money, but it can also burn a lot of money.