Sounds like you may be really starting from scratch on your learning. It would be best to work entirely inside a VPN like tailscale for complex apps like jellyfin if you want them. You can set up https, but there’s no harm either way. You might not use your own domain right away inside your VPN, but you will a little down the road. You will get annoyed with using IP addresses for your services and set up an internal DNS server eventually. You can safely experiment and make mistakes inside your tailnet.

For learning to set up an open Internet exposed service, use a completely isolated, dedicated computer (maybe a raspberry pi on a demilitarised zone of your internet router or better yet a $5 VPS on someone else’s network). Then read up on hosting a “static website” with either ngnix or Caddy. I prefer the latter because one short config file can set everything up for https and take care of the certificates for you. This can eventually become the gateway into your other services from the open Internet, but do not do that from the start, just a simple personal website. This will require learning a little Linux system admin, SSH (read up on key based authentication so you can disable password authentication in SSH), remote file management, and configuring a webserver, DNS, and certificates. Lots to learn.

Because it is just hosting static webpages, theres almost no risk of it being hacked and used maliciously if you misconfigrure something or forget to patch it. Static sites are awesome nowadays anyway, though, you don’t even really need a fancy site generator to get started, just some simple HTML files. A fun and easy project is a hand written list of your favourite web links and then set your browser’s new tab page to it. Instantly useful and fully under your control.

I actually envy your spot on your learning journey. It was such a rewarding experience for me to do all the above.