The tables in this appendix list the most useful Lisp packages that come with Emacs. All Lisp packages are typically located in the directory emacs-source/lisp, where emacs-source is the directory in which you placed the Emacs source distribution. We have omitted all of the packages that provide "basic" Emacs support; likewise, we have omitted many packages whose functionality is obsolete or unspeakably obscure.
While some of these packages are described in some detail in this book, most aren't; you will have to rely on GNU Emacs' help for precise descriptions of what the package does. See Chapter 14 for details about help; the most important help commands you will need for finding out about the functionality of Lisp packages are C-h p (for finder-by-keyword), C-h f (for describe-function), and C-h m (for describe-mode).
C-h p is especially helpful. It lets you navigate through a hierarchy of information about all packages available on your system, from general areas of functionality, like those in the tables in this appendix, to the C-h m information about each individual mode. Unfortunately, the detailed information is sometimes incomplete and also lists many packages that could not possibly be interesting to anyone other than hard-core Emacs customizers.
Wherever it is reasonable, the tables in this appendix give commands that "start" the package. This startup information has the following meanings:
If the package implements a major mode, the startup ...