> I am looking up documentation for emacs-version. But cannot understand the
> meaning of
> 
> If optional argument HERE is non-nil, insert string at point.
> 
> --------
> Doc:
> 
> (emacs-version &optional HERE)
> 
> Probably introduced at or before Emacs version 19.20.
> 
> Return string describing the version of Emacs that is running.
> If optional argument HERE is non-nil, insert string at point.

This is the doc string for Emacs 27.2 (the latest release):

  Return string describing the version of Emacs that is running.
  If optional argument HERE is non-nil, insert string at point.
  Don’t use this function in programs to choose actions according
  to the system configuration; look at ‘system-configuration’ instead.

But it's still a poor doc string.  It should, first
of all, describe the interactive use.  It should say:

  With a prefix argument, insert string at point.
  ^^^^^^^^^^^^^^^^^^^^^^

Only after that interactive description should it
give the Emacs-Lisp description of argument HERE:

  When called from Lisp, optional argument HERE
  corresponds to the prefix argument.

Consider filing a (doc) bug report for this:
`M-x report-emacs-bug'.