Where can I find additional contributions to qualified retirement accounts?

What type of account did you contribute to?  401k, traditional IRA, Roth IRA?

401k

traditional IRA

traditional IRA

To enter contributions to a Traditional IRA in TurboTax, please follow these steps:

1. Click on Federal > Deductions & Credits 
2. Scroll down to the Retirement and Investments section and click on the Start/Revisit box next to Traditional and Roth IRA Contributions.  [See Screenshot #1, below.]
3. On the Traditional IRA and Roth IRA screen, mark the box for Traditional IRA and click Continue.  [Screenshot #2]
4. On the screen, Did you Contribute to a Traditional IRA?  click the Yes box.  [Screenshot #3]
5. Click the appropriate box on Is This a Repayment of a Retirement Distribution?  [Most likely,it isn't.] [Screenshot #4]
6. On the Tell Us How Much You Contributed screen, enter the amount of your contribution and click Continue.  [Screenshot #5]
7. Continue through the screens, entering the requested information

If you're referring to 401k contributions, TurboTaxMargaretL provides a good explanation:

Any employer - sponsor retirement contributions are already listed on your W2, box 12.  Entering W2 form into Turbo Tax exactly as it appears is the only entry required. 

The 401(k) plan contributions you elect to make come directly out of your salary. Since the contributions are made with pre-tax dollars, your employer does not include these amounts in your taxable income for the year. At the end of the year, when you receive your W-2 form that shows your earnings, you will notice that your wages subject to federal income (box 1) tax are lower because of your 401(k) contributions (box 12). Since the contributions are not counted in your taxable income to begin with, you do not take a deduction when you file your return.