Here is how to add your gambling activity in TurboTax Online:
Click on Federal Taxes, Wages & Income, Wages & Income Summary > Add more income > Less Common Income > Gambling Winnings > Start or Revisit
Enter the information from the W-2G. If you do not have a W-2G, choose that you did not receive one and proceed to enter the winnings. Continue through the interview to add losses. You can deduct gambling losses as an itemized deduction up to the amount of your gambling and prize winnings.