Honestly I'd start at irs.gov.  The 1040 instructions and Pub 17 will get you off the ground.

Here's Pub 17:

https://www.irs.gov/pub/irs-pdf/p17.pdf

And a preview of the draft instructions for 2020 Form 1040:

https://www.irs.gov/pub/irs-dft/i1040gi--dft.pdf

If you need a cure for insomnia, you can also read the entire Internal Revenue Code on the Cornell University website:

https://www.law.cornell.edu/uscode/text/26

Welcome to the asylum.

Rick