Assuming that you're referring to the Motor Vehicle Excise Tax you paid on a vehicle in Massachusetts, you enter this in the federal section of TurboTax Online:
- Select Tax Home in the left pane
- On the Hi, let's keep working on your taxes! screen, select the dropdown on the right side of the Deductions & Credits box, then select Start, Continue, or Pick up where you left off
- On the Your tax breaks page, scroll down and select the dropdown to the right of Cars and Other Things You Own
- Select Start or Revisit to the right of Car Registration Fees
- Answer Yes on the Did you pay any car registration fees in 2023? page
- Provide all relevant information requested in the interview
See the TurboTax Help article Is my car registration fee deductible? for more information.
If you're referring to something else, feel free to post back.