in org-mode, how to insert timestamp with today's date?

Question

In a Lisp function, how do I instruct org to automatically insert a timestamp with today's date?

I found the function org-insert-time-stamp, but I don't know how to provide an argument for it that will return today's date.

The documentation for the function says:

(org-insert-time-stamp TIME &optional WITH-HM INACTIVE PRE POST EXTRA)  

...but I don't see where to find documentation about what TIME &optional WITH-HM INACTIVE PRE POST EXTRA means or how to specify these in a function.

And here's the function I'm trying to write:

(defun org-today-heading-and-clock-in ()
  "Insert a new heading with today's date, and then clock in."
  (interactive)
  (org-insert-subheading)
  (org-insert-time-stamp (today))
  (org-clock-in))

Answer 1

With a bit of guesswork:

(org-insert-time-stamp (current-time))

Answer 2

I am using the following two functions with different timestamp formats. The number of digits to be used in year ie 2015 or 15 and hours, minutes, seconds etc can also be specified.

(defun now ()
  "Insert string for the current time formatted like '2:34 PM' or 1507121460"
  (interactive)                 ; permit invocation in minibuffer
  ;;(insert (format-time-string "%D %-I:%M %p")))
  ;;(insert (format-time-string "%02y%02m%02d%02H%02M%02S")))
  (insert (format-time-string "%02y%02m%02d%02H%02M")))

(defun today ()
  "Insert string for today's date nicely formatted in American style,
  e.g. Sunday, September 17, 2000 or standard 17-09-2000."
  (interactive)       ; permit invocation in minibuffer
  ;;(insert (format-time-string "%A, %B %e, %Y")))
  (insert (format-time-string "%d-%m-%y")))

Answer 3

I get a time stamp using {{{date}}}