These are bilateral contracts and each contract is unique in terms of size, date, asset size and quality. The contract price is not transparent as it is not publicly disclosed. While in futures contract, trades take place on the exchange and the terms are standardised by the exchange. Gearing is leveraging of results where initial cash-flow in taking a position is less than the value of the position. Higher the gearing, higher the risk.
Index is an indicator of the broad market.
It is a weighted average of prices of select stocks, where the weight is the market capitalization of individual stocks. Market capitalization is the product of stock price and number of shares issued by the company. The contracts themselves are often traded on the futures market, which is a market in which contracts for future delivery of a commodity or a share are bought or sold. These are future contracts where it is the index which is bought or sold. Instead of buying shares that constitute the Index, one buys the market by taking a position on the Index future.