Are you referring to withholding from your place of employment? If so, this will appear on your W-2 (Box 15, 16 and 17), and be entered in the Federal - Wages and Income section of TurboTax when you enter your other W-2 information.
To add a second line for a second state's withholding, click on the Add Another Line button underneath Box 15 on the W-2 entry screen.
If this does not fully answer your question, kindly provide additional details below.
