I learned this from Jeffry Ritcher (https://www.amazon.com/CLR-via-C-Developer-Reference-ebook/d...)
A lot of what I know about C# is from his books. I wish every language had someone of his caliber write a book about it.
I think the version of the book I read was "CLR via c#" about 10 years ago
If you're a real OG, you used `ildasm`.