As others have mentioned (and also explained in quite some detail) you're trying to bite off a lot at once. First, for Jellyfin locally you can ignore most of that.
And if you really want to learn the ins and outs of all that (and I can recommend it, it's useful), then I suggest you start with some simple web app. Something like note taking or maybe even something trivial like a whoami service, which basically just echos some information it was sent back to you. That's super useful because you know that it is unlikely to be broken, so you can focus on the networking/port forwarding issues. And once you've got that working and have a rough feeling how this all works you can go on to more complex setups that actually do something useful.