C-h b
This opens the help showing the correspondence between key-bindings and elisp functions.
Look for
C-x C-f
in it (you can do it by typing C-s C - x space C - f), you find find-file. Now, do
C-h f find-file
and it tells you, among other things, the syntax :
(find-file FILENAME &optional WILDCARDS)
So just try
(find-file "/path/to/your/file")
in your .emacs