If you imported a W-2 and TT won't let you change it, you may have to delete the W-2 and re-enter it manually.
Boxes 18-20 are for local (city, county, school district, other) income taxes. You should know whether you pay was subject to local withholding. Boxes 18-20 are blank for most people. There should ever be a 0 in box 20.
