There is no TDS (Tax Deduction at Source) for your stock market gains in the US. So when you make money and send it back to your Indian bank account, the broker in the US does not deduct any tax on it. You will have to pay Short-term Capital Gains Tax OR Long-term Capital Gains Tax in India, whatever is applicable. Short-term Capital Gains apply if a security is held for less than 36 months.
A 30% TDS applies only on your dividend earnings. This is when stocks in your portfolio give out dividends to their investors.
US and India have a Double Taxation Avoidance Agreement (DTAA). This means that you pay tax only once. For the TDS done on your dividend earnings, you will get W-8BEN from DriveWealth. You can use it while filing your taxes in India to show that you have already paid taxes on this income. W-8BEN can be issued whenever you request.