What the File does not give me breacrumbs

That’s plugin for Theme authors and editors, for easy access to theme files. Sounds like 100% not for you.

Where do I insert the code?

You don’t.

For example, I am told that after enabling “What the File,” I have to add the code to my theme’s template

Umm, who told you that? Where? For what reason?

Elsewhere, I am told to go to the Dashboard and click on “Design” and then “Theme Editor.” But there are no such options on my Dashboard.

I’m 100% sure, that this is totally out of scope of this plugin.

I read that if I hover over “What the File” on my toolbar, I should see “single.php.” However, I see “page.php” and “Template Parts” and Content-page.” Now what???

Yep. That’s the thing, that this plugin should do – it should tell you which templates of your theme was used to render that specific page (and it showed you).

I am told to NEVER edit PHP files from within WordPress, that I have to have FTP access. Even HostGator cannot tell me how to get FTP access.

And I can agree with anyone who give you that advice – if you don’t know PHP you can break something in serious way.

It seems to me that What the File should give clear instructions as to what to do after downloading it.

What The File adds an option to your toolbar showing what file and template parts are used to display the page you’re currently viewing.

↑ not clear enough? That’s first sentence of plugin description. Still the same as 3 years ago.

You’ve wrote review of wrong plugin.