Hi,
The Closing Price of a scrip is calculated as the weighted average of the last 30 minutes of trading in the scrip. A picture of the closing price of the day is calculated and explained here.
The Opening Price of a scrip is the equilibrium price decided by bids and offers made in the Pre-open market. The Equilibrium price in a scrip is then calculated as the price at which maximum buy and sell quantities can be matched.
To read more about the Opening-price and the Pre-open market, do read this link.