The practice documented here is all about developing bash shell functions. In my opinion, the use of functions in bash, while readily accessible, is under-appreciated, under-used. Pick one of these approaches to the material, based on your needs and interests.
If you are interested in a more formal approach, choose this reading sequence:
The Tag Manual discusses uses of a new feature introduced here, the null-command comment. The tag was introduced mostly to provide the shdoc feature, internal documentation, motivated by traditional languages, javadoc, pydoc, …
If you have some shell programming experience, choose this order:
While the material here is not for the beginning shell programmer, the author recommends his e-book Shell Functions, which has a link to a series of YouTube videos on the method. Visiting the videos, you will find a host of other introductions to the shell.