Explain Like I'm 5 (ELI5)

Back in the day, your ISP would have a Usenet server. Maybe they still do. I haven't looked into it in a very long time. It would be something like nntp://news.timewarner.com, and you would add that to your email client of all things, because newsgroups were glorified email lists. Your email address was your identity, and you sent messages to groups. The protocol was different, but you were basically sending emails. Then your message would be shared to news servers all over the world. A giant peer-to-peer network. It worked a lot like Lemmy, sort of. Not really.

If ISPs do host news servers nowadays, it's going to be censored and definitely won't be hosting petabytes of binary files. If they host binary files at all, they won't be particularly fast to download, and will probably be limited to images and such.

A modern usenet provider costs money per month because they host all of those files, with very long retention times. Years and years. Plus they have insane download speeds. Do you have gigabit fiber at home? Cool! Enjoy downloading these files with a full speed direct download. That's what the provider gives you. Access to the "real" Usenet, for a long time, with excellent download speeds. This costs real money, so you pay for this service per month. Providers have different tiers of service, too, with various limits. It's like picking a phone plan.

Second, you need an indexer. A different website that tells you where the files are. Otherwise, good luck finding them. Imagine trying to find a specific meme on Lemmy by just browsing all the meme communities and scrolling and scrolling. The indexer is a search engine for these files, neatly organized categories. Indexer websites cost a one-time small fee per year.

You download "nzb" files from the indexer. Those small files contain a long list of all the files to go download. You see, every binary file available for download is split into dozens of small RAR files, or some other format. So, thing.rar, thing.r00, thing.r01 thing.r02, etc. The nzb file contains metadata for the download plus a link to each of those files in whatever newsgroup they are in. I imagine whole seasons of individual episodes can be stuffed into a single nzb file, too, but I'm just guessing.

You use bespoke software to manage the downloading and rebuilding of all of those pieces. An nzb file will open in this program to manage the download. There are FOSS ones available, I'm sure, but also paid ones, and even ones for phones.

(If I got parts of this wrong, please forgive me. I have never used any of these things. Well except for newsgroups way back in the 90s.)