So ...

Basically, the plugin adds a new drop-down menu to your admin toolbar showing what file and template parts are used to display the page you’re currently viewing. Simple as that ...

And the plugin works out of the box, so there are no settings for you to configure. Upon activation, you can visit your site to see the plugin in action.

Simply move your mouse over to the "What The File" menu item, and you'll see the aforementioned drop-down menu showing the template files used to display that given page.

Here's the live result on my homepage ...

... and here's the result on my post page:

It's simple, efficient and very useful.

OK. Now let's see some closing thoughts ...