You have to open the Demat account at any broking site like Angel Broking, Sharekhan, Motilal Oswal etc.
Link that Demat account to your bank account and do all the necessary paperwork.
You can do intraday trading or long term investment. First, you should study the stock, its performance on various parameters and how it performed in 1 week, 14 weeks, 52 weeks.
And then you can start trading through the app or website or services of your particular broker.
We would suggest you to use moneycontrol.com
and angel broking.