* stk. price
Strike price is exercise price of the underlying. To put it other way, the strike price is the price which you believe that the underlying will reach and go above, so your profit will start only after the spot price reaches the strike price. 5200 is strike price in this example.
* Spot Price
The prevailing market price of the underlying NIFTY/stock.
* Interest Rate
Risk free interest you would earn if you have invested in an instrument which is risk free. Generally it is fix deposit interest which is considered as Risk Free. Concept here is that if you are earning 6% return without taking any risk, then the return should be good enough to allow you to worth the risk your taking for buying the option instrument.
* Div. Yield
If underlying stock is paying dividend in the month which you are trading then Div. Yield is to be considered in the formula, as the dividend pay out will effect the stock price. In index options it is always 0.
* Volatility/Premium
While calculating option price, either you enter prevailing premium of the selected or you enter volatility of the selected option. If you enter prevailing premium the calculator will calculate volatility. And if you know volatility of the selected option , the calculator will calculate the option premium for you.
Here in the example ask price of the 5200 option Rs.31-50 is entered.
* I hope number of days is the days in which the option is going to expire
Yes
* I hope Premium is the amount which i pay to buy the options.
Premium as explained above if calculate it will allow to know what would be the fair premium of the selected option and you can compare with the actual premium prevailing in the market
*What are these? Delta, Gamma, Theta, Vega, Rho
These are options Greeks. However I would suggest that you search in Google for "Option Greeks" to get the idea on each of these Greeks, as it is also difficult for me to explain each one. Following are few useful links..
http://www.theoptionsguide.com/the-greeks.aspx
http://www.investopedia.com/articles/optioninvestor/04/121604.asp
I am also learning option trading, therefore I would also request the seniors to correct me if wrong.