Cash futures is quite simple. Reliance is trading at Rs.2100 in the cash market and at Rs.2118 in the 1-month futures. You buy Reliance in cash equivalent to the lot size and sell one lot of Reliance futures.
At a conceptual level, arbitrage is the anomalies in pricing. In the good old days of the NSE and BSE, there used be huge price differences between the two exchanges and even with the regional exchanges.