First of all, please familiarize yourself with options in this blog post.
I’ll summarize it here. A call option gives the buyer the right to purchase 100 shares of a stock.
Let’s say you own 1 AAPL call option at strike price $200, that means you can buy the 100 shares of AAPL at $200. If the AAPL price at that time is $250, it means you can pocket $50 per share. That’s $5000. Now, if the AAPL price is at $150, you’ll lose $5000 instead.