All of Emacs's help is under C-h by default.
C-h C-h (Control-H, pressed twice) brings up the menu, the most useful ones are in bold.
For example, to figure out what a key does, press C-h k (key combination).
|a PATTERN||command-apropos. Give a substring, and see a list of commands (functions interactively callable) that contain that substring. See also the apropos command.|
|b||describe-bindings. Display table of all key bindings.|
|c KEYS||describe-key-briefly. Type a command key sequence; it prints the function name that sequence runs.|
|C PATTERN||describe-coding-system. This describes either a specific coding system (if you type its name) or the coding systems currently in use (if you type just RET).|
|d PATTERN||Show a list of functions, variables, and other items whose
documentation matches the PATTERN (a list of words or a regexp).
|e||Go to the *Messages* buffer which logs echo-area messages.|
||describe-function. Type a function name and get documentation of it.|
|F COMMAND||Display the frequently asked questions file.|
Display information about the GNU project.
|h||Display the HELLO file which illustrates various scripts.|
|i||info. The info documentation reader. This is where the Emacs manual is.|
|I METHOD||describe-input-method. Describe a specific input method (if you type its name) or the current input method (if you type just RET).|
|k KEYS||describe-key. Type a command key sequence; it displays the full documentation.|
|K KEYS||Show the Emacs manual’s section for the command bound to KEYS.|
|l||view-lossage. Show last 300 characters you typed.|
|L||describe-language-environment. This describes either a specific language environment (if you type its name) or the current language environment (if you type just RET).|
|m||describe-mode. Print documentation of current minor modes, and the current major mode, including their special commands.|
|n||view-emacs-news. Display news of recent Emacs changes.|
|p||finder-by-keyword. Find packages matching a given topic keyword.|
|s||describe-syntax. Display contents of syntax table, plus explanations.|
|t||help-with-tutorial. Select the Emacs learn-by-doing tutorial.|
||describe-variable. Type name of a variable; it displays the variable's documentation and value.|
||where-is. Type command name; it prints which keystrokes invoke that command.|
|C-a||Information about Emacs.|
|C-c||Emacs copying permission (GNU General Public License).|
|C-d||Instructions for debugging GNU Emacs.|
|C-e||External packages and information about Emacs.|