"Kodi", as installed fresh and new, is simply a music and video player. It does not come with any content at all.
BUT, because it is totally open source, a community has grown up around it, creating sub-programs, if you will, which bring free content by scraping the web (and likely the dark web) for movies, tv shows and music. These add-ons, like Kodi, have no content of their own, but they sure know where said content is located and are more than happy to direct Kodi to it.
If you have ever gone to a website looking for free tv episodes, you have likely had contact with this community. Kodi simply made all this better organized and cross platform.