options selling

If I sell a 17400 NIFTY PE at Rs.40 and collect 2000 premium and it expires at strike price of 17300 then as a seller, how much do I have pay as my option expired in the money? And what if it expires out of the money? (In the above example instead of 17300 it expires at stirke price of 17500)

I heard about this strategy where you can sell puts with 30 or so days to expiration and pocket a premium every month. Has anybody tried this If someone has tried it then I would like to know the how far did they sell the option and in which stock they tried it.