There are no apparent instructions anywhere, including right here on the plugin page, on how to use this thing. But having been there and done that, I looked to see if anything had been added to the post edit page and low and behold a YouTube Thumbnail button had been added to the editor toolbar.
When clicked, a window pops up with a place to put the video ID.
Once inserted into the post, the shortcode produces a page (post) that looks just like the screenshot, with the video thumbnail and description. The thumbnail has a little play button that, when clicked, pops out a lightbox player.
It does not respond to mobile displays, but the thumbnail shows up, and the player did play on the mobile device, taking up the entire screen, but only displaying about a third of the video image (at least it was centered).
Anyway, for the most part, on my setup, it did what it said it would do.
I do wish there was a way of straightening out the thumbnail so it isn't rotated. It's kind of a catchy look, but it would be nice to be able to have a straight forward look as well.