If you are e-filing you do not mail anything. If you are mailing your return, on paper then you need to attach copies of documents showing tax withheld, such as W-2's and 1099R's.
To enter your 1099R
Go to Federal> Wages and Income>Retirement Plans and Social Security>IRA 401 k) Pension Plan Withdrawals to enter your
1099R.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**