Beginning in tax year 2018 the IRS has introduced new schedules due to the Tax Cuts and Jobs Act (tax reform). Schedule 1 represents additional income and adjustments to income. This schedule reflects many of the line items that used to represent the top half of Schedule 1040 such as taxable refunds, business income, unemployment compensation etc. If you have any of those items, you would be required to file Schedule 1. Please see the link below for Schedule 1 items.
https://www.irs.gov/pub/irs-pdf/f1040s1.pdf