I read the post on "how to style". How do I find the single-listing.php?

I've read the "How to Style" the Directory.

But I'm a newbie and know nothing about PHP.

I would like to have a basic layout like the one in the video.

So at least please let me know how to get to the "single-listing.php" as it says?

I clicked on:

Plugins/
Directory/
Edit/
but couldn't find any single-listing php file.

Thanks,
Mark