How do I close an automatically opened window in Emacs?

Using winner mode, you can use the keybinding C-C left arrow to return to the previous window configuration. Of course, this doesn't actually kill the new buffer, but it does hide it.

I'm usually using the delete-other-windows command. C-x 1.

It's so regullar, that I rebinded to F4.

Official docs: https://www.gnu.org/software/emacs/manual/html_node/emacs/Change-Window.html#Change-Window

HTH

From what I understand, you want to close the buffer in the other window without moving your cursor from the current window.

I don't any existing function does that, so I rolled my own.

(defun other-window-kill-buffer ()
  "Kill the buffer in the other window"
  (interactive)
  ;; Window selection is used because point goes to a different window
  ;; if more than 2 windows are present
  (let ((win-curr (selected-window))
        (win-other (next-window)))
    (select-window win-other)
    (kill-this-buffer)
    (select-window win-curr)))

You can bind it to something like "C-x K" or some other somewhat difficult-to-press key so you won't press it by mistake.

(global-set-key (kbd "C-x K") 'other-window-kill-buffer)

I use this a LOT! (for Help buffers, Compilation buffers, Grep buffers, and just plain old buffers I want to close now, without moving the point)

At least here on my emacs (22.3), when the debugger pops up, its window becomes the active one. There, pressing q just quits the debugger, if that's what you want. At that point, it also gets out of recursive editing.