shortening long posts

I can’t quite figure out how to edit the_content to enable long posts to display with a “read more” link.

My index.php file for the template reads
<?php the_content(‘Read the rest of this entry »’); ?>

But, when I put the <!–more–> tag in a post (not sure if that’s what I’m supposed to do, since I’m a newbie, so let me know if I’m doing this incorrectly), the post doesn’t shorten.