Minimum margin for NIFTY FUTURE(NF) is 21 K, and that for MINI NIFTY FUTURE(MNF) is 8.2 K. For risk management reasons, you will broker will require that you need have atleast 25 K and 10 K in your account for NF and MNF respectively.
Premium and discount: In simple terms, it is the difference between the value of the FUTURE contract and its underlying. For NF and MNF, the underlying is S & P CNX NIFTY (NIFTY) index. For ex: If NIFTY is trading at 5100 and NF is trading at 5106, i.e. 6 points higher than its underlying, we say as "Premium of 6 points". Similarly, if NIFTY is trading at 5100 and NF is trading at 5097, the we say as "Discount of 6 points".