wp does not match with the DOC

Hi there,
I’ve downloaded 3.9.2 and attempted to modify the header image. It seems that the description in the documentation has nothing to do with the current directory structure and file content of wp. Each references to wp directories php and css file names, content, markups are wrong. Ok, it’s open source… but still… this is below the line. Rgds, Janos

e.g.: a structure like this:

#header {
background: url(“<?php bloginfo(‘stylesheet_directory’); ?>/images/wc_header.jpg”)
no-repeat bottom center; }
#headerimg {
margin: 7px 9px 0;
height: 192px;
width: 740px; }

in wp theme twenty twelve can not be found at all.

Is there anybody out there who can tell me, how can I add a 1050×192 px header image to the twenty twelve theme?
Many thnks, Janos