A quick run down: Get yourself a Usenet client (akin to qbittorent for example). SABnzbd is the most popular, free, and open source.

Next you will need an Indexer (similar to a torrent site like The Pirate Bay). There are a lot of these and you will usually need to pay (most are like 10-20 per year, some are free, but it may be hard to find content on the only free sites) to access an indexer. A good paid one I used was NZBgeek. Another is NZB Finder which has free accounts (with some restrictions).

Last thing you need is a Usenet Provider (these are the companies that actually host the files you download). You will need to pay for this for sure and most people actually pay for 2-3 Usenet providers (most only host things for a certain time and content can get taken down due to DMCA). There are a ton of options to choose from and you can mix and match is so many diffrent ways, but Frugal Usenet is pretty popular (if you pay for yearly, they give you an account for another Usenet provider that you can use as a partial backup). I always paired it with UseNight (just has speed restrictions depending on time, but its a great backup) which is very cheap per year. I don't want to get to technical, but I will mention it incase people want to take the Usenet dive. When buying multiple providers, do NOT buy them if they are from the same backbone! You can refer to this chart to help figure out the main ones. Content that gets taken down via DMCA is pretty much removed at the backbone level and will affect every provider under it (I know the free account from Frugal is the same backbone, but that's just for backup in case of outages).

Sorry just getting used to notifications in lemmy so I didn't see this till now. But @hydra@beehaw.org summed it up perfectly.

You need A client, an indexer, and a Usenet provider.

I use SABnzbd for my client, I've got several different index sites, and 3 providers. One of which is a yearly unlimited subscription and the other 2 are bucket plans where I buy access to a set amount of GB to download and once I use it, I either buy more or lose access. They basically serve as backup servers if something can't be found on my main unlimited server. I use prowlarr in conjunction with radarr and sonarr to manage my indexers and shows and movies, and use SABnzbd as my download client, connected to my Usenet provider. It works beautifully once you get it set up right.