The definitive reference is Apple's own Inside Macintosh. Many parts of that are still available on the Apple developer web site, e.g. https://developer.apple.

The definitive reference is Apple's own Inside Macintosh. Many parts of that are still available on the Apple developer web site, e.g. https://developer.apple.com/library/archive/documentation/mac/pdf/MacintoshToolboxEssentials.pdf https://developer.apple.com/library/archive/documentation/ma... https://developer.apple.com/library/archive/documentation/mac/pdf/MoreMacintoshToolbox.pdf https://developer.apple.com/library/archive/documentation/ma... For a more directed and more C-oriented walkthrough, the Macintosh C Programming Primer was a pretty common go-to. It's been out of print for ages, of course, but there's a PDF available at: https://vintageapple.org/macprogramming/pdf/Macintosh_C_Programming_Primer_1992.pdf https://vintageapple.org/macprogramming/pdf/Macintosh_C_Prog...