For the purposes of this explanation sonarr and radarr are the same, but keep in mind that sonarr only does tv shows and radarr only does movies

You tell sonarr what you want to watch --> sonarr tells prowlarr what you want to watch --> prowlarr will search websites for magnet links to your show (you have to specify which websites) --> prowlarr will give the download manager (qbittorrent, etc) the magnet link and it will download it --> sonarr will take the downloaded file and copy it somewhere else for organizational purposes --> media server (jellyfin) will see the copied file and download associated metadata (thumbnail, episode name, episode number, etc) and allow you to watch it

The only programs you need for a purely functional arr stack are sonarr/radarr, prowlarr, qbittorrent, and jellyfin, or any other media server. Anything else is purely icing on the cake