It's kinda complex.
Jellyseerr let's you browse movies by grabbing movie and TV show info from TheMovieDB.
Once you see something you like you hit "Request " and then Jellyseerr sends the movie info to Radarr (for movies) or Sonarr (for TV shows)
Radarr and Sonarr ask Prowlarr to find a torrent, and then they send that torrent magnetic link to qBittorrent.
qBittorent then starts the download. Once qBittorrent finishes, Radarr or Sonarr rename the files properly and copy them to a folder that Jellyfin sees.
The originsl torrent files are left for qBittorrent to continue sharing, so you will have two copies of the torrent files until you delete the torrent and files from qBittorrent, leaving only the copy for Jellyfin.
whew... that's a lot going on.