I've been using a "Kodi box" I ordered from Amazon for at least a couple years. It's basically a very simple computer that runs Android as its Operating System. Think of it as an Android tablet but you need to connect it to a TV. You can run most Android apps, and Kodi is one of them.
Kodi is the new name for XBMC. The developers changed the name a few versions ago because it had evolved so far from XBox that the name didn't make sense anymore. Some argue that the new name doesn't make sense either.
It is basically a media player. You point it to media sources and it creates menus, thumbnails, plot rundowns etc. It's just a nice interface for browsing a media library.
Kodi itself doesn't have any media files included with it and the application developers officially condemn using it illegally. But of course, many people use it for viewing illegally downloaded files and many of the available addons will stream content directly from internet sources. With these addons, you don't even have to download a file before playing it.
If you have some movies or TV shows downloaded, you can install Kodi on your PC and try it out. You'll be able to get a feel for the software and decide whether you want to use it on a TV. The software is free, and the addons are free, so if you're curious, go for it.
The new version (v17) looks really great. I'm still using 16.1 because my Android box needs an OS upgrade before I can run the new one, but i've played with it on my PC.
I think quite a few of us here use Kodi, so if you have questions, you're sure to get some answers.