Including showauto-php string in esplandae

i want to connect categories with pages. so i installed page2cat-plugin.
i connected the pages with the categories but now i have to copy&paste a php string you can find here ( http://dev.swergroup.com/pages-and-posts-shortcodes/wiki/showauto ) into the category.php template.

can you help me with that? do not find the category.php data. what is its name in esplanade?