The dark green box indicates that a topic has been completed and the light green box indicates that more information is needed where you started a topic but did not complete it. The gray boxes represent tax topics you have not yet visited in the TaxCut interview. TaxCut will not let you click on a gray topic to prevent you from skipping around your tax return and forgetting to complete a topic.
Take Me To is useful for checking on data you have entered or adding data that you missed entering previously. Other than this, you really do not need to navigate around your return since TaxCut's interview will ensure that all tax topics that pertain to you are completed.
Next: TaxCut Help Center

