You would have received a Welcome letter & Email from HDFC Securities with the Login / Username details post account opening. Incase you have not received the same; you can contact customer care (link of customer care page) for retrieving the same.
Click on the TRADE NOW button which is available on the top hand band on right side on website. Enter username/Login id & continue with entering the password.
One can instantly generate the password Online by following the below steps.
Step 1: Enter Username/ Login id & Bank Customer id (Mandatory fields)
Step 2: Enter your HDFC Net Banking Password (received in Net Banking Kit)
Step 3: Enter your new trading password.
You can place a request with contact customer care department (https://www.hdfcsec.com/article/customercare-3105) for a fresh password. You would receive the same within 7 working days.