What does it mean that I have to file a schedule 1

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You have an entry on this form  https://www.irs.gov/pub/irs-pdf/f1040s1.pdf

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Schedule 1 is used when you have additional income, such as capital gains, unemployment compensation, prize or award money, gambling winnings. 

And/or, if you have any deductions to claim, such as student loan interest deduction, self-employment tax, educator expenses.

Please see Schedule 1, Additional Income and Adjustments to Income to see all the information that might be included there.