#Syntax
(defun command-name (args)
"documentation" (interactive "template")
body)
#Example
(defun this-line-to-top-of-window (line)
"Reposition current line to top of window.
With prefix argument LINE, put point on LINE."
(interactive "P")
(recenter (if (null line)
0
(prefix-numeric-value line))))
The interactive spec says how to read arguments interactively. Type C-h
f
interactive RET
for more details.