Assuming you operate on a calendar year (which you do unless you formally elected some other fiscal year) and are a cash basis tax payer (which, again, you are unless you formally elected to be an accrual based taxpayer) you pay tax based on income actually received, vs income expected.
So, for example, Amazon pays 2 months in arrears. In November you get September's earnings; in December you get October's earnings. Both of those will be this year's income. November's and December's earnings won't be paid until January and February of next year, so they'll be next years' earnings. Conversely, if you've been doing this a while, earnings from LAST November and December (2019) would have been paid to you in January and February of 2020. So they should also be included on your 2020 tax return.
I suppose if you're paying quarterly based on what you earned that quarter (rather than based on a calculation adjusted from your 2019 numbers) you'd want to include in the 4th quarter the amounts that hit your account, or were at least available to you, in October, November, and December.
When deciding what to pay, don't forget to adjust for allowed expenses, and don't forget that you owe income tax and ALSO self-employment tax (social security/medicare) at a rate of around 15%.
If you need professional help, here are a couple of websites to find a qualified tax professional (who may or may not be an accountant) in your area.
www.natptax.com
www.naea.org
(n.b. I'm an Enrolled Agent in good standing with the IRS, though currently retired.)