Tony Aldon has an interesting post on reddit that discusses the implementation of Org speed keys. That doesn’t seem like it would be all that interesting but it turns out to be more complex and involved than you might think, involving—among other things—the self-insert function that places characters you type on the screen and in the buffer.
Aldon does a really nice job of walking us through the code to show us how things really work. You need to be at least a little familiar with Elisp to understand the flow but it’s worth the effort. On the one hand, an Emacs user doesn’t really need to understand any of this to effectively use Emacs but understanding how things works makes Emacs less opaque and easier to reason about.
The nice thing about posts like Aldon’s is that they introduce us to the workings of Emacs a little bit at a time. By taking tiny bites, we’re not overwhelmed by what is, after all, a pretty complex program. It’s a fairly long post but if you want to increase your understanding of how Emacs works, it’s well worth your time.