When the minibuffer is in use, it appears in the echo area, with a
cursor. The minibuffer starts with a prompt, usually ending
with a colon. The prompt states what kind of input is expected, and
how it will be used. The prompt is highlighted using the
minibuffer-prompt face (see Faces).
The simplest way to enter a minibuffer argument is to type the text, then RET to submit the argument and exit the minibuffer. Alternatively, you can type C-g to exit the minibuffer by canceling the command asking for the argument (see Quitting).
Sometimes, the prompt shows a default argument, inside parentheses before the colon. This default will be used as the argument if you just type RET. For example, commands that read buffer names usually show a buffer name as the default; you can type RET to operate on that default buffer.
If you enable Minibuffer Electric Default mode, a global minor mode,
Emacs hides the default argument as soon as you modify the contents of
the minibuffer (since typing RET would no longer submit that
default). If you ever bring back the original minibuffer text, the
prompt again shows the default. Furthermore, if you change the
minibuffer-eldef-shorten-default to a non-
value, the default argument is displayed as ‘[default]’
instead of ‘(default default)’, saving some screen space.
To enable this minor mode, type M-x
Since the minibuffer appears in the echo area, it can conflict with other uses of the echo area. If an error message or an informative message is emitted while the minibuffer is active, the message hides the minibuffer for a few seconds, or until you type something; then the minibuffer comes back. While the minibuffer is in use, keystrokes do not echo.