Your employer will report in box 12 of your W-2 your contributions to the SIMPLE 401(k) plan.  Enter the box 12 amounts only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax.  TurboTax will use this information to prepare your tax return.  You employer will already have reduced the taxable income in box 1 of your W-2 by the amount of your elective deferrals to the SIMPLE 401(k), so you don't get to deduct that amount again.

Distributions from the SIMPLE 401(k) plan will be reported to you and to the IRS on Form 1099-R that you'll need to enter into TurboTax.