They're just media library organizers that can download media for you using torrents or Usenet. There's a different one for each type of media:

• Radar - Movies
• Sonarr - TV
• Lidarr - Music
• Readarr - eBooks
• Whisparr - Porn

There's also prowlarr, which you can use to set up a list of indexers (torrent/Usenet sites) that the other *arr servers can use, so you don't have to configure each server's indexer list individually. You can also use it as an aggregated indexer search for other things that arent managed by the rest of the suite (like software).

There's also bazarr which you can use to automatically download subtitles for your TV/movie library.

And there's flaresolvarr which can be used by prowlarr to bypass captchas for indexers that use them.

It's all pretty easy to set up, especially if you're using docker containers, although there is a community install script that'll do everything for you if you want them installed directly on Linux.

You do need a separate download client set up, like qbittorrent for torrents and sabnzbd for Usenet.

have you already given trash guides a read? it helped me be able to conceptually put the pieces together a little better. it still took actually setting them up and using them for a bit to really understand certain aspects of them, or see 'why' certain things are how they are when I'd previously had no clue for some settings.

They don't need necessarily need a Usenet account, They can work perfectly well with ordinary torrents.