The following briefly details the commands that are available while input is being read in the echo area.

C-f (echo-area-forward)
Moves forward a character.
C-b (echo-area-backward)
Moves backward a character.
C-a (echo-area-beg-of-line)
Moves to the start of the input line.
C-e (echo-area-end-of-line)
Moves to the end of the input line.
M-f (echo-area-forward-word)
Moves forward a word.
M-b (echo-area-backward-word)
Moves backward a word.
Cd (echo-area-delete)
Deletes the character under the cursor.
Del (echo-area-rubout)
Deletes the character behind the cursor.
C-g (echo-area-abort)
Cancels or quits the current operation. If completion is being read, C-g discards the text of the input line which does not match any completion. If the input line is empty, C-g aborts the calling function.
RET (echo-area-newline)
Accepts (or forces completion of) the current input line.
C-q (echo-area-quoted-insert)
Inserts the next character verbatim; for example, so you can insert control characters into a search string.
printing character (echo-area-insert)
Inserts the character.
M-Tab (echo-area-tab-insert)
Inserts a Tab character.
Ctrl-t (echo-area-transpose-chars)
Transposes the characters at the cursor.

M-d (echo-area-kill-word)
Kills the word following the cursor.
M-Del (echo-area-backward-kill-word)
Kills the word preceding the cursor.
C-k (echo-area-kill-line)
Kills the text from the cursor to the end of the line.
C-x, Del (echo-area-backward-kill-line)
Kills the text from the cursor to the beginning of the line.
C-y (echo-area-yank)
Yanks back the contents of the last kill.
M-y (echo-area-yank-pop)
Yanks back a previous kill, removing the last yanked text first.

Sometimes when reading input in the echo area, the command that needed input will only accept one of a list of several choices. The choices represent the possible completions, and you must respond with one of them. Since there are a limited number of responses you can make, info allows you to abbreviate what you type, only typing as much of the response as is necessary to uniquely identify it. In addition, you can request info to fill in as much of the response as is possible; this is called completion.

The following commands are available when completing in the echo area.

Tab (echo-area-complete)
SPACEBAR
Inserts as much of a completion as is possible.
? (echo-area-possible-completions)
Displays a window containing a list of the possible completions of what you have typed so far. For example, say the available choices are the following if you typed an ‘f’, followed by ‘?’.

bar foliate 
food forget

Possible completions would contain the choices which begin with ‘f’.
 
foliate food forget
 
Pressing Spacebar or Tab would result in ‘fo’ appearing in the echo area, since all of the choices which begin with ‘f’ continue with ‘o’. Now, typing ‘l’ followed by pressing Tab results in ‘foliate’ appearing in the echo area, since that is the only choice which begins with ‘fol’.
Esc Ctrl-v (echo-area-scroll-completions-window)
Scrolls the completions window, if that is visible, or, if not, the other window.