Are you asking about this for tax year 2020 or for tax year 2021---which will be filed in early 2022?
You have self-employment income. You are REQUIRED to file a tax return if you have received even $600 of self-employment income. Forget about $20K or 200 items----that is not the rule you have to worry about. That is the rule e-Bay has to worry about. YOU have to file, and YOU have to keep good records for yourself of how much you made, how much you spend for expenses (goods, shipping, packing materials, etc. etc.) You are motivated and enterprising enough to make $20K so you are also mature enough and smart enough to learn the rules for preparing and filing your taxes. Awesome!
Who has to file?
http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return%3F
https://ttlc.intuit.com/questions/2903027-how-do-i-report-income-from-self-employment
https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922
https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax
https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c
https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct
https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs
You say that you are a "minor" which suggests that someone else (parent?) can probably claim you as a dependent on their own tax return. On your own return you have to say that you can be claimed as a dependent.
https://ttlc.intuit.com/community/dependents/help/when-do-i-have-to-answer-yes-to-being-claimed-as-a...
It is too late to start a 2020 tax return using online TurboTax. You will need any version of the CD/download for 2020 in order to prepare your tax return. You have to prepare a Schedule C to enter your expenses. Any version of desktop software can do that.
CD/DOWNLOAD (This requires a full PC or Mac—-cannot be used on a mobile device)
https://turbotax.intuit.com/personal-taxes/cd-download/
You can also purchase the CD/download from various retailers such as Costco, Amazon, Walmart, Best Buy, Staples, Sam’s Club, etc. etc. etc.
This link Where can I obtain authentic TurboTax software? has a list of authorized TurboTax resellers.
If you are actually asking about filing a 2021 return---which you cannot do yet----then when online software for 2021 is available you need the version called Self-Employed, or any version of the CD/download.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
