Amanbhati
In simple terms : Margin is the deposit you keep. Leverage is what you get to transact in return.
E.g To buy BankNifty Futures of 25 lot size @ 17,680, you will need a margin (deposit with the broker) of approx. 35,500 to carry fw. a trade overnight. While the actual value of the trade is 25*17,680 = 442,000.
Leverage is the exposure/power/advantage that you get. In the above case, 442,000 minus 35,500 is the leverage i.e 406,500
The ratio of leverage or exposure would be 442,000/35,500 i.e 12.45