Read more tag

Hi, everyone.
I have a problem with the read more tag. I put it at the end of the paragraph, I then continue writing but it simply does not show. I read the problem is that there’s a piece of code to be placed somewhere in order to let it show on pages.
this one exactly:

<?php
global $more;
$more = 0;
?>
//The code must be inserted ahead of the call the_content, but AFTER the_post()

<?php the_content(‘Continue Reading’); ?>

In ypour opinion in which .php file I need to put it? Because until now, I was not successful!
Thank you.