Arsh,
Just a simple analogy. E.g a newly constructed building has a value (Cost + labour) of X amount. Say this is the 'value' of the building, and is represented as same as 'Spot Nifty' Now the owner wants to sell it. Surely he will not want to sell at cost, but rather at a premium. But what price will the property attract? This will be based on the 'trend' If real estate prices are on the upswing, the owner will want a premium. And if the prices are on a down swing, the seller will want a discount. Consider the price the building gets transacted 'As Nifty futures' This price is a consensus price of the buyer and seller....
So to answer your question, futures prices take into account trend, expectations, volatility, demand-supply, greed and fear etc.... The same principal (in my view) determines Index or Stock futures trade.... and Nifty Spot follows these unquantified view of the market participants.....
Trust this helps....