1) IF you are talking about your "Contributions" done thru your workplace payroll deductions....then those are entered with your W-2 information....and nowhere else in the software.
2) If you are talking about your distributions/income from taking $$ out of a 401k, then those are entered in the retirement 1099-R section on the Wages&Income menu page of the TTX software.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*