The document explains how derivative contracts work in the stock market through an example. It describes a scenario where an investor buys a futures contract for Stock A at Rs. 120, with settlement in 5 days. Each day, the investor's account is credited or debited based on whether the stock price increased or decreased from the previous day. At settlement, the stock price was Rs. 125, so the investor gained Rs. 5 total. However, since the investor only paid 15% margin money of Rs. 18 upfront, the effective return on investment was 27%.