Emacs provides extensive help features accessible through a single character, C-h. C-h is a prefix key that is used only for documentation-printing commands. The characters that you can type after C-h are called help options. One help option is C-h; that is how you ask for help about using C-h. To cancel, type C-g.
C-h C-h displays a list of the possible help options, each with a brief description. Before you type a help option, you can use SPC or DEL to scroll through the list.
C-h means "help" in various other contexts as well. For
example, in query-replace, it describes the options available.
After a prefix key, it displays a list of the alternatives that can
follow the prefix key. (A few prefix keys don't support this because
they define other meanings for C-h.)
Here is a summary of the defined help commands.
command-apropos).
describe-bindings).
describe-key-briefly). Here c stands for `character'. For more
extensive information on key, use C-h k.
describe-function). Since commands are Lisp functions,
a command name may be used.
info).
The complete Emacs manual is available on-line in Info.
describe-key).
view-lossage).
describe-mode).
view-emacs-news).
finder-by-keyword).
describe-syntax). See section The Syntax Table.
help-with-tutorial).
describe-variable).
where-is).
info-goto-emacs-command-node).
info-goto-emacs-key-command-node).
The most basic C-h options are C-h c
(describe-key-briefly) and C-h k (describe-key).
C-h c key prints in the echo area the name of the command
that key is bound to. For example, C-h c C-f prints
`forward-char'. Since command names are chosen to describe what
the commands do, this is a good way to get a very brief description of
what key does.
C-h k key is similar but gives more information: it displays the documentation string of the command as well as its name. This is too big for the echo area, so a window is used for the display.
C-h c and C-h k work for any sort of key sequences, including function keys and mouse events.
C-h f (describe-function) reads the name of a Lisp function
using the minibuffer, then displays that function's documentation string
in a window. Since commands are Lisp functions, you can use this to get
the documentation of a command that you know by name. For example,
C-h f auto-fill-mode RET
displays the documentation of auto-fill-mode. This is the only
way to get the documentation of a command that is not bound to any key
(one which you would normally run using M-x).
C-h f is also useful for Lisp functions that you are planning to
use in a Lisp program. For example, if you have just written the
expression (make-vector len) and want to check that you are using
make-vector properly, type C-h f make-vector RET.
Because C-h f allows all function names, not just command names,
you may find that some of your favorite abbreviations that work in
M-x don't work in C-h f. An abbreviation may be unique
among command names yet fail to be unique when other function names are
allowed.
The function name for C-h f to describe has a default which is
used if you type RET leaving the minibuffer empty. The default is
the function called by the innermost Lisp expression in the buffer around
point, provided that is a valid, defined Lisp function name. For
example, if point is located following the text `(make-vector (car
x)', the innermost list containing point is the one that starts with
`(make-vector', so the default is to describe the function
make-vector.
C-h f is often useful just to verify that you have the right spelling for the function name. If C-h f mentions a default in the prompt, you have typed the name of a defined Lisp function. If that is all you want to know, just type C-g to cancel the C-h f command, then go on editing.
C-h w command RET tells you what keys are bound to
command. It prints a list of the keys in the echo area. If it
says the command is not on any key, you must use M-x to run it.
C-h w runs the command where-is.
C-h v (describe-variable) is like C-h f but describes
Lisp variables instead of Lisp functions. Its default is the Lisp symbol
around or before point, but only if that is the name of a known Lisp
variable. See section Variables.
A more sophisticated sort of question to ask is, "What are the
commands for working with files?" To ask this question, type C-h
a file RET, which displays a list of all command names that
contain `file', including copy-file, find-file, and
so on. With each command name appears a brief description of how to use
the command, and what keys you can currently invoke it with. For
example, it would say that you can invoke find-file by typing
C-x C-f. The a in C-h a stands for `Apropos';
C-h a runs the command command-apropos.
Because C-h a looks only for functions whose names contain the string which you specify, you must use ingenuity in choosing the string. If you are looking for commands for killing backwards and C-h a kill-backwards RET doesn't reveal any, don't give up. Try just kill, or just backwards, or just back. Be persistent. Also note that you can use a regular expression as the argument, for more flexibility (see section Syntax of Regular Expressions).
Here is a set of arguments to give to C-h a that covers many
classes of Emacs commands, since there are strong conventions for naming
the standard Emacs commands. By giving you a feel for the naming
conventions, this set should also serve to aid you in developing a
technique for picking apropos strings.
char, line, word, sentence, paragraph, region, page, sexp, list, defun, rect, buffer, frame, window, file, dir, register, mode, beginning, end, forward, backward, next, previous, up, down, search, goto, kill, delete, mark, insert, yank, fill, indent, case, change, set, what, list, find, view, describe.
To list all Lisp symbols that contain a match for a regexp, not just the ones that are defined as commands, use the command M-x apropos instead of C-h a. This command does not check key bindings by default; specify a numeric argument if you want it to check them.
The super-apropos command is like apropos except that it
searches documentation strings as well as symbol names for matches for
the specified regular expression.
The C-h p command lets you search the standard Emacs Lisp libraries by topic keywords. Here is a partial list of keywords you can use:
bib.
C-h i (info) runs the Info program, which is used for
browsing through structured documentation files. The entire Emacs manual
is available within Info. Eventually all the documentation of the GNU
system will be available. Type h after entering Info to run
a tutorial on using Info.
There are two special help commands for accessing Emacs documentation
through Info. C-h C-f function RET enters Info and
goes straight to the documentation of the Emacs function
function. C-h C-k key enters Info and goes straight
to the documentation of the key key. These two keys run the
commands Info-goto-emacs-command-node and
Info-goto-emacs-key-command-node.
If something surprising happens, and you are not sure what commands you
typed, use C-h l (view-lossage). C-h l prints the last
100 command characters you typed in. If you see commands that you don't
know, you can use C-h c to find out what they do.
Emacs has numerous major modes, each of which redefines a few keys and
makes a few other changes in how editing works. C-h m
(describe-mode) prints documentation on the current major mode,
which normally describes all the commands that are changed in this
mode.
C-h b (describe-bindings) and C-h s
(describe-syntax) present other information about the current
Emacs mode. C-h b displays a list of all the key bindings now in
effect; the local bindings defined by the current minor modes first,
then the local bindings defined by the current major mode, and finally
the global bindings (see section Customizing Key Bindings). C-h s displays the
contents of the syntax table, with explanations of each character's
syntax (see section The Syntax Table).
You can get a similar list for a particular prefix key by typing C-h after the prefix key. (There are a few prefix keys for which this does not work--those that provide their own bindings for C-h. One of these is ESC, because ESC C-h is actually C-M-h, which marks a defun.)
The other C-h options display various files of useful
information. C-h C-w displays the full details on the complete
absence of warranty for GNU Emacs. C-h n (view-emacs-news)
displays the file `emacs/etc/NEWS', which contains documentation on
Emacs changes arranged chronologically. C-h t
(help-with-tutorial) displays the learn-by-doing Emacs tutorial.
C-h C-c (describe-copying) displays the file
`emacs/etc/COPYING', which tells you the conditions you must obey
in distributing copies of Emacs. C-h C-d
(describe-distribution) displays the file
`emacs/etc/DISTRIB', which tells you how you can order a copy of
the latest version of Emacs. C-h C-p (describe-project)
displays general information about the GNU Project.