This tool provides a simplified income tax calculation.
There tax forms shown in the "Input Forms" section is where you normally enter the information for your tax return. There are other forms in the "Additional Tax Forms" section where you can also enter information, but these are not normal input forms. When you enter information on one of these forms, it will override the value that would normally be calculated for that field. For example, if you enter a value in form 1040, line 1a for wages, the tool will no longer calculate that value from the values it finds on W-2 forms.
The remainder of this document describes the fields that are computed (blue) and the fields where you can enter data (green). The fields are listed in the same order as they appear in the tool. This is also the same information that is displayed in the tool tips.