Thank you, Urquhart1244 for responding.
I looked at the Apple Support documents you linked me to and couldn't quite figure out how to "sync" movies between my Mac and my iPad mini. But it did make me look at my iTunes app, and there I saw some "home movies" that also appeared on my iPad.
So . . . I went to File | Add to Library ... on iTunes on my Mac Mini. Then I found the file using the directory and added the video file (mp3) to my iTunes library.
Next I connected my iPad mini to my Mac Mini, using a USB cable so that the iPad was linked to iTunes. In the iTunes "Home Videos" library, I found the video. I dragged and dropped the video icon onto my iPad Mini and voila . . .
I opened the AppleTV app on my iPad, checked the "Home Videos" library, and there was the video that was on my Mac Mini.
The Apple Support documents didn't really tell me how to do this, but they (and you) reminded me about syncing and iTunes, so what I needed got done.
Simplified explanation:
Import the video to the iTunes Library on my Mac Mini.
Connect my iPad to iTunes on the Mac Mini.
Drag and drop the video icon onto my iPad.
AppleTV now has the video in its library, and I can manage and use it (and other "home videos") through AppleTV.
And it just occurred to me . . . Is there a way to use the AppleTV on my iPad and just download "Home Video" files from, say, DropBox or my iCloud Drive? I don't see it.