SQ is currently $68 and I own 100 shares. Say I will sell you the right to buy 100 SQ from me for $10. The deal is you buy 100 SQ at $70/share next Friday.
SQ over 70 ->
Buyer (you): You get to buy 100 SQ from me at $70. Wit a $10 premium, your effective price is
SQ under 70 but above initial price -> Buyer: Call is worthless. (loses value initially paid) Seller: Keep premium and the 100 shares of SQ. (this is best outcome)
SQ drops from initial price -> Buyer: Protected from losses of owning the stock. Call is worthless. Seller: Incurs losses from stock, but keeps premium and shares. (premium reduces total losses) (second best outcome)