Most of the time, "commissions" are considered self-employment income. You'll likely receive a 1099 (tax document) from Amazon reporting your income. But you'll need to keep excellent records of this income, as well as any business expenses associated with this income.
Unless something changes with the TurboTax Free Edition, you will not be able to use the Free Edition to file your tax return for 2019. You'll be required to upgrade to a paid edition. At a minimum, you'll be required to use the Deluxe Edition, and possibly upgrade to Self Employed Edition. The TurboTax program (you can always begin with Free Edition) will direct you on preparing your 2019
tax return in early 2020.
You also need to educate yourself on making quarterly estimated tax payments, as income taxes and self-employment taxes on these commissions are expected to be paid throughout the year. You should review IRS Publication 1040-ES and familiarize yourself with your obligations. I've linked the publication below.
https://www.irs.gov/pub/irs-pdf/f1040es.pdf
*** I am NOT a tax expert. I am a seasoned TurboTax user, and volunteer to provide assistance to TT users. Nothing I post is to be considered TAX ADVICE; I bear no legal liability for responses.***
