When I started back in the dark ages, we had two free IRS pubs that contained virtually everything you need to know to get your introductory education.

IRS PUB 17

IRS PUB 334 You will need to check back to get the updated 2021 edition

Bookmark these or call to get real honest to goodness paper copies to leaf through https://www.irs.gov/forms-pubs/forms-and-publications-by-us-mail