If I buy January 2016 nifty futures contract and I make 200 points gain on the contract in the current month itself , so can I sell them in the current month or I have to wait till next month ?
Your question is very amateurish.I suggest to get some working knowledge before starting trading in indian markets.
Go though the below link.
Anyhow the answer for your query is one can buy and sell anytime if it is avavilable to trade.
At any point of time, you can always buy or sell futures of current month, next month and far month. (Currently Dec-15, Jan-16 and Feb-16) provided they are being actively traded. Generally Index futures are most actively traded than stock futures. Same applicable for options.
And yes I am reading Zerodha Varsity. Just started 2 days back.