What is a call option, in plain words?
A call option is a contract that gives you the right, but not the duty, to buy 100 shares of a stock at a set price (the strike) until a set date (the expiry). You pay for that right up front (the premium). If the stock ends above the strike, the call is worth the difference; if it ends at or below, it expires worth nothing and you lose what you paid, and no more.
Try it: a call with a $50 strike, bought with 30 days left at 30% implied volatility (made-up numbers). Move where the stock ends at expiry.
Simulated example, priced by the StrikePath engine (Black–Scholes, interest 4.3% a year). For learning; not advice.
Why people buy calls
A call lets you take part in a rise for less money up front than buying the shares, with a loss limited to what you paid. The price of that is that the stock has to rise far enough, soon enough: above the strike plus what you paid, by expiry, for the call to end with a gain.
Before expiry
Until it expires, a call is worth more than what it would pay right now, because the stock still has time to move. That extra is time value. It shrinks every day, and it moves with the size of swing the market expects (implied volatility). That is why a call can lose value even when the stock rises a little.
What this shows, and what it doesn't
The value at expiry for one contract, before fees and the bid-ask spread. Real options are quoted per share and traded in contracts of 100 shares. Selling (writing) a call is a different trade with a different risk: its loss has no ceiling.