Futures & Options are derivative instruments and it is nothing but getting Rights to Buy & Right to sell from Sellers & Buyers. Strike price is nothing but the amount agreed to buy and sell at the time of signing the contract. If the stock price goes above the strike price call option buyer will get profit and if the stock price goes below the strike price put option buyer will enjoy the money. Call option seller will enjoy the premium when the price does not cross above the strike price and put option seller will enjoy the premium when the price does not cross below the strike price. Premium is nothing but the amount decided by the buyer to sign the contract at sellers end.