What does the numbers at the top mean when it says "Federal Due"?

This would indicate that your withholding and other tax payments made throughout the year are not sufficient to pay your taxes for the year.  

If you've finished entering all of your data, TurboTax will assist you with the different options available to make your payment to the IRS during the final steps. If you've not finished entering all of your tax information, this number may change as your return is finalized. 

You will have until April 15 to pay the tax due without incurring any interest or penalties.  If you're not able to pay the tax in full by that time you should still file the return as there are separate penalties for paying late and filing late, and the penalties for filing late are steeper.