A dialog box is a special kind of menu for asking you a yes-or-no question or some other special question. Many Emacs commands use a dialog box to ask a yes-or-no question, if you used the mouse to invoke the command that led to the question.
To disable the use of dialog boxes, change the variable
use-dialog-box to nil. In that case,
Emacs always performs yes-or-no prompts using the echo area and
keyboard input. This variable also controls whether to use file
selection windows (but those are not supported on all
platforms).
A file selection window is a special kind of dialog box for
asking for file names. You can customize the variable
use-file-dialog to suppress the use of file
selection windows, even if you still want other kinds of dialogs.
This variable has no effect if you have suppressed all dialog
boxes with the variable use-dialog-box.
When Emacs is compiled with GTK+ support, it uses the GTK+
file chooser dialog. Emacs adds an additional toggle button to
this dialog, which you can use to enable or disable the display
of hidden files (files starting with a dot) in that dialog. If
you want this toggle to be activated by default, change the
variable x-gtk-show-hidden-files to t.
In addition, Emacs adds help text to the GTK+ file chooser
dialog; to disable this help text, change the variable
x-gtk-file-dialog-help-text to nil.