Hi,
If you are talking about trading Nifty Futures for intraday, then you have to first add Nifty Future to your watchlist. You can add the current month contract as it will be the most actively traded.
Once its added, you can open the order window and either buy or sell depending on the position you want to take. Since you wish to do intraday, you have to use MIS(Margin Intraday Squareoff) as your product type.
You can also trade with Nifty Call and Put options on an intraday basis.