You can start selling your holdings right away if these shares do not belong to the T2T (Trade-to-trade) category. 

You can go to your holdings by clicking the button below, select the share you intend to sell, Click on the sell button and proceed with the sale. 

It is possible that sometimes the "Sell" button is grayed out. This happens when you just bought T2T category stocks. 

To sell these stocks, you will have to wait till they get delivered to your Demat account as per the SEBI regulation which takes 1 trading day, from the date you place a successful buy order.