The HyperCard Users Guide was good, but it was after my uncle loaned me his copies of "The Complete Hypercard Handbook"[0] and "HyperTalk 2.0 The Book" that I really got obsessed. I was 9 years old and reading these thick tomes cover to cover, and building test stacks for each obscure function. The code examples were full of jokes that were way over my head but I loved it nontheless (or maybe that's part of why I did love it).
https://archive.org/details/The_Complete_HyperCard_Handbook