I'm not sure if the piracy megathread or FMHY megathread cover the *arr stack specifically, but they have lots of information so I'm recommending them broadly for anyone wanting to ingest information about piracy.

Regarding what the arr stack even is:

Tldr, you set up a list of public and/or private trackers in Prowlarr or Jackett. In Radarr and Sonnar you set up movies and shows respectively that you want to keep track of. Rad/Sonarr check those trackers for releases for your tracked media matching criteria (like resolution, size, language, etc).

When it finds a matching release, it sends the torrent file or magnet link to your torrent client to download. When it finishes, Rad/Sonarr hardlink or copy the file to a library location and organize/name them according to rules you set.

You can point Jellyfin or Plex to that library location and all the media will be organized so it can easily figure out what media is there and grab metadata for it (cover images, description, ratings, etc). Then you can watch that media through Jellyfin/Plex or an app that plugs into them.

The *arrs also work with usenet if you'd prefer that over or in addition to torrenting with a vpn.