There are numerous ways to find it. Often you can login to your router, and find it there. There are Windows, Linux and Mac commands available -- so this is something you can ask Google or ChatGPT to find for you.
Some LANs don't have a local domain name set, and in those cases you can't refer to anything on your LAN by name, everything has to be done by IP.
EDIT: Also, as I said it's optional.









