Futures contract is a contract where the buyers and sellers are executing a contact when the stock reaches agreed strike price on a particular day the buyer is liable to buy that particular stock and seller is supposed to sell the particular stock . If price increase the seller is supposed to settlemet for the amount of increment the same is applicable in case of price decrease for buyer to settle.
In future and options markets settlements are done through cash only, in order to take the advantage of particular stock in a market the buyer and sellers are executing the trade by paying the margin amount