Radar and Sonarr are tools to track movies and TV shows respectively. You can add a movie/show to track, tell it the quality you want it in, and set up Prowlarr or Jackett to give Son/Radarr the access to the torrent trackers it needs. You can also use Usenet but I have no experience there.
It will search those torrent trackers for releases matching your movies/shows in the quality and language you set for them and send the downloads to the torrent client you set up. When the client finishes downloading, Son/Radarr copies (or hardlinks) the files to your library folders.
If Son/Radarr is tracking a show that you currently have downloaded in 480p, but the quality profile allows upgrades up to 1080p, it will search for 720p and 1080p releases and pick the best match it can find. When the torrent client finishes downloading it, Son/Radarr will automatically replace the 480p release with the 1080p release it just downloaded.
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.