So, Jellyfin is one of those apps where the Docker documentation is really lacking. I'm gonna give you my docker-compose.yml file in case it helps:

services:
  jellyfin:
    image: jellyfin/jellyfin
    user: 0:0
    restart: 'unless-stopped'
    ports:
      - '8096:8096'
    environment:
      #- JELLYFIN_CACHE_DIR=/var/cache/jellyfin
      #- JELLYFIN_CONFIG_DIR=/etc/jellyfin
      - JELLYFIN_DATA_DIR=/var/lib/jellyfin
      - JELLYFIN_LOG_DIR=/var/log/jellyfin
    volumes:
      - ./config:/config
      - ./cache:/cache
      - ./data:/var/lib/jellyfin
      - ./log:/var/log/jellyfin
      - /data/jellyfin:/data/jellyfin
    devices:
      - /dev/dri

For me /data/ is my RAID array, which is why my jellyfin data directory is there. Everything else goes in the same directory as the compose file. My system has a graphics card that does transcoding (Arc A380), so I have /dev/dri under devices.

You should learn a lot about Docker Compose, because it will help you tremendously. I use Jellyfin behind an Nginx Proxy Manager reverse proxy. I'd highly recommend it. Here's my compose file for that:

services:
  app:
    image: 'jc21/nginx-proxy-manager:latest'
    restart: unless-stopped
    network_mode: "host"
    #ports:
    #  - '80:80'
    #  - '81:81'
    #  - '443:443'
    volumes:
      - ./data:/data
      - ./letsencrypt:/etc/letsencrypt

Running in "host" mode is important, instead of just forwarding ports, because it lets you forward things to localhost, like pointing https://media/.[mydomain]/ to http://127.0.0.1:8096/ for Jellyfin.

Anyway, best of luck to you, and I hope that helps!