F&O future &options you seem to be using only future
long=buy
short=sell but upto expiry for that month then either you have to roll over or square up your position,
ask your broker to long or short nos. of lots
lot for nifty= 50 units
minifty= 20 units
bank nifty=50
for stocks lot size refer to nseindia
for payment we generally pay 10-15% of total amount i.e. for nifty 25000-30000
for mininifty 10000.