Cannot put movie files into Plex

Any time I look try to add a movie file to Plex, it’s greyed out and refuses to allow me to select it. Please tell me what I need to do to get movie files into Plex, all the Googling I’ve done hasn’t helped at all.

I have no idea what the tags mean, but it wouldn’t let me create the topic without picking one so I just picked the top one, “server-windows”…it’s probably not remotely relevant to my problem.

You don’t add files into Plex.
You add a folder with several files in it.

https://support.plex.tv/articles/categories/your-media/

https://support.plex.tv/articles/201543057-why-is-some-of-my-content-not-found/