adding author name to blog post in template

Hi WordPressers,
I have a very rudimentary understanding of all things code and web, but enough to tinker around. I’m stumped for the moment, and though I’ve read everything I can in the Codex, I must be missing something.

I’m using a theme and want to add the name of the author to single blog posts. When I add

<p>Written by:
<?php the_author_posts_link(); ?></p>

All that shows up is “written by:” Author names are used elsewhere in the theme, but I can’t get them to work here.

What am I missing?

Thanks!