If you made 401k contributions thru payroll deferrals, that amount will be reflected on your W-2 box 12 as code "D" and TurboTax will read that code and factor it into the Retirement Saver's Credit calculation (the only potential credit for those contributions). So you won't need to enter anything else off your statement.
If you made contributions to Traditional or Roth IRAs, then -- if you haven't already done so -- you'll enter the amount(s) in the Deductions & Credits section by clicking on Retirement and Investments, then Traditional and Roth IRA Contributions, and follow the prompts. TurboTax will ask you a series of questions to determine the contribution amount(s) allowed and their deductibility (for the Traditional IRA). Both Trad & Roth IRA contributions will be factored into the Retirement Saver's Credit calculation.
