The core idea
A call gives the buyer a right to buy the underlying asset under contract terms. The seller can have an obligation if assigned.
A little more context
A put gives the buyer a right to sell. It has a premium, strike price, expiration, and contract-specific terms.
What to remember
The buyer pays the premium; the seller receives it in exchange for obligations. Contract multipliers affect total dollar cost.
Pause and reflect: how would you explain this idea to someone who has never invested?