A call option is a contract that gives you the right to buy 100 shares of a stock at a specific price before a specific date. You pay a premium for this right. If the stock rises above that price, you can profit. If it doesn't, you lose the premium and nothing else.
That's the entire concept. Everything else is details.
The underlying stock. This is the stock the option is based on. When you buy a call option, you're buying the right to purchase 100 shares of that stock.
The strike price. This is the price at which you can buy the stock. If you hold a $200 call, you have the right to buy 100 shares at $200 regardless of where the stock is actually trading.
The expiration date. This is the deadline. After this date, the option ceases to exist. If the stock hasn't moved above your strike by expiration, the option expires worthless.
The premium. This is what you pay for the option. It's determined by the stock price, the strike price, time until expiration, and implied volatility. The premium is your maximum risk.
You profit on a call option when the stock price rises above the strike price by more than the premium you paid.
If you buy a $200 call for $5.00 per share ($500 total), your breakeven is $205. The stock needs to be above $205 at expiration for you to make money. At $210, you profit $5 per share ($500). At $220, you profit $15 per share ($1,500). There's no cap on how high it can go.
If the stock stays at or below $200 at expiration, the option expires worthless and you lose the $500 premium. The stock could drop 50% and your loss is still $500 — not the full value of 100 shares.
Leverage. For $500 (the premium), you control the upside on $20,000 worth of stock (100 shares × $200). If the stock rises 5%, you might make 100%+ on your option.
Defined risk. Your loss is capped at the premium. No margin calls, no forced liquidation, no risk of losing more than you paid.
Flexibility. You can sell the option at any time before expiration. Most traders never exercise — they sell the option itself for a profit when it gains value.
Time. More time until expiration means a more expensive option. The stock has more opportunity to move, so the option is worth more. This value decays every day (theta decay), accelerating in the final 30 days before expiration.
Volatility. Higher implied volatility means more expensive options. If the market expects the stock to make big moves — earnings, FDA decisions, product launches — options cost more because the probability of a large move is higher.
Distance from the stock price. The further the strike is from the current stock price, the cheaper the option. A strike close to the current price costs much more than one far away, because the closer strike is much more likely to be profitable by expiration.