How can I use fuction "append-to-buffer"?

[Wu XiaoGuang <xgwu@linux.net.cn>]

Hi,all:
  I am reading Emacs Lisp Intro.
  There is one fuction:

(defun append-to-buffer (buffer start end)
       "Append to specified buffer the text of the region.
     It is inserted into that buffer before its point.

     When calling from a program, give three arguments:
     a buffer or the name of one, and two character numbers
     specifying the portion of the current buffer to be copied."
       (interactive "BAppend to buffer: \nr")
       (let ((oldbuf (current-buffer)))
         (save-excursion
           (set-buffer (get-buffer-create buffer))
           (insert-buffer-substring oldbuf start end))))

  I want to know how can I use it?
  Thank you.