Each buffer in Emacs is in a (single) major mode. Different kinds of buffer have different major modes. For example, if you edit an EmacsLisp file, the major mode (by default) is
emacs-lisp-mode. The mode for a file is determined by the SetAutoMode function.
Each major mode customises Emacs’s behaviour to make it appropriate for the type of buffer by providing appropriate commands, display and key bindings. For example, in emacs-lisp-mode, commands are available that are appropriate to editing EmacsLisp code. In DiredMode, commands are available for manipulating files and directories. Major modes often have SyntaxHighlighting for the visually unimpaired.
The name of the current major mode is displayed in the mode line. You can change to a different major mode by executing its command. For TextMode (indicated by “Text” in the mode-line), for example, do
‘M-x text-mode’. You can use
‘C-h m’ for help on the current major mode, and
‘C-h b’ to see all the bindings in effect. The symbol identifying the current major mode is stored in the variable
Although many major modes ship with Emacs, sometimes you will need to download an elisp package off the Internet and install it. See InstallingPackages.
There are also minor modes. Minor modes are orthogonal to major modes. There can be any number of minor modes in a buffer.