Might be a surface-level pull, but a lot of languages have 'by example' guides that walk you well-documented code. I have really fond memories of reading through an early copy of Rust by Example[0] in high school, which really opened my eyes and helped me understand The Rust Book better. A little while ago I had to learn Go in a short time, and Go by example[1] was equally as helpful for getting me up-and-running!
for me it isnt the code, so much as what the code is manipulating.
having a firm grasp on the standards and specifications of any given file structure is indispensible. same goes with CPU , storage controllers and memory
when you know these things about hardware, then you have opportunity to see why code must obey certain majik rules.
[0] https://doc.rust-lang.org/stable/rust-by-example/
[1] https://gobyexample.com/