My W2 in boxes 18 and 19 are 2 different dollar amounts. How should I select one or both?

Is there a locality name in box 20?

Boxes 18-20 are for local tax.   Unless you have such a local tax then if there is no locality name in box 20, boxes 18 &19 should be blank.  Sometimes employers improperly place other data in those boxes because they think that they are unused boxes, but might cause the TurboTax review to flag it as an error.    Ask your employer if box 20 is blank.

You will enter these two items separately.  

box 18 is income you earned. 

Line 19 is income tax you paid.  

In the W-2 input screen of the TurboTax program, you will see there is a box to enter each number.