The most common way to find immediate help with commands and programs in Linux is to attempt a program --help or man command in the terminal. However, some of the most extensive resources are found by means of info. These extensive resources are scarce: info is available only for the elite.
Info command and directory
Info is like man, only it documents fewer commands and programs with greater verbosity. Typing info in the terminal followed by Enter returns the complete Info documentation directory. In Linux, the directory is located at (or close to) /usr/share/info.
The viewer that is opened by info is Emacs-like. Navigate with arrows and spacebar, follow links with Enter. To move “up directory” i.e. radically towards the root of the documentation, hit u as many times as needed. To close the thing, the keybind is C-x C-c or, thankfully, q.
To navigate the viewer in Vi-like manner, open it with info --vi-keys. To close Info when it has been opened with Vi keys, type :q. For more info on Info, type info info.
Info on and in Emacs
Since the viewer is Emacs-like, it makes sense that the most extensive Info manual is about Emacs. To view the Emacs manual without searching the full Info directory, start Info by typing info emacs. For information on another useful little editor, try info nano. Unfortunately info vim and info vi only return the respective man pages, no additional manuals.
Since the viewer is Emacs-like, Emacs fans may want the full Emacs to view the Info directory. For this, there is M-x info inside Emacs. Now you see the same directory for the most important GNU programs, commands, and libraries, but within full-blown Emacs!
You are quite right.
Some –help files are good but most seem to be summaries of the man files, which are much more extensive.
The only thing is they can be awkward to navigate for the novice Linux user.
Even though I was brought up on Clipper (Intergraph unix) and regarded myself as a reasonably proficient user that was almost 30 years ago. Today even I find man files daunting.
I revert to them only if I can’t find what I need I need in –help.