An option is a one-page contract between two people. It fixes four things: the underlying (100 shares of a stock), the strike price written in ink, the expiry date, and the premium — the market's price for the contract itself, paid up front by the buyer to the seller and never refunded.
The word that names the instrument is the buyer's right, not obligation, to use it. A call is a price-lock coupon to BUY at the strike: gold if the stock climbs above it, binned if it doesn't. A put is the right to SELL at the strike — insurance on a stock, a floor under a position. A buyer's maximum loss is always the premium, because walking away is free.
The question beginners rarely ask is who takes the other side. Every option has a seller whose obligation mirrors the buyer's right: if the holder exercises, the seller must deliver or buy at the strike, no exceptions. Sellers volunteer for the same reason insurance companies exist — the buyer pays for certainty, and the seller gets paid, up front and every time, to carry risk.
The interactive machine in the lesson makes the core decision physical: a $100-strike option, a Call/Put flip, and a stock-price slider that swings the verdict between exercise and walk away while the option's expiry value updates live. One contract covers 100 shares, so a $2.50 premium is $250 of real money.
Educational, not investment advice.