You should have received a 1099R for it.  If not, ask the employer or plan for it.

The easiest way to get to the 1099-R entry screen is to simply search for 1099-R (upper- or lower-case, with or without the dash) in your TurboTax program and then click the "Jump to" link in the search results.

Enter a 1099R under
Federal Taxes on the left side
Wages & Income at the top

Then scroll way down to Retirement Plans and Social Security,
Then IRA, 401(k), Pension Plans (1099R) - click Start or Revisit

If you are filing a Joint return be sure to pick which person it is for.