The help system is largely based on the Info file format, which GNU Emacs uses for on-line documentation. When accessed by following a menu entry or a cross reference, the help system will locate the corresponding Info node. When accessed by keyword search, an ad-hoc menu will be created instead.
If you are running outside Emacs, the information will be displayed on
the terminal, controlled by the environment variable PAGER.
If you are running under Emacs, Emacs will try to use the Info subsystem
as far as possible. If Emacs is unable to find the Info nodes
requested, or when displaying an ad-hoc menu, it displays the
information in a buffer where specialized key bindings apply as
summarized in ref-olh-hlp. The most important key binding is
?, which will display the appropriate key-binding summary. After
typing a question mark, typing a b will get you back to where you
were.
The organization of the help files corresponds directly to that of the printed manual. Files that do not begin with a menu correspond to leaf nodes of the manual tree; that is, to sections of the manual that have no subdivisions. Files that do begin with a menu correspond to the non-leaf nodes of the tree.