Self-hosting domain question

I have been reading the Bitwarden website on self hosting. I’m not sure if I want to self host on a Raspberry Pi or Linux on Proxmox. Any advice would be great.

But I’m totally confused about the domain part. I signed up for Bitwarden some time ago but have not gotten around to migrating to it. But the Bitwarden internet service I only want to use on the devices I take out the house.

For everything else I just want a self hosted internal server that I don’t want to be exposed externally. That is simply because I have a lot of devices in my home that I never take out and masses of passwords that I never use externally.

So, what I’m not understanding is what I need to do with regard to a domain name for that given that I don’t want external access.

Sorry if that is a dumb question but I can’t make sense of it. I watched some videos that talk about reverse proxies and web servers and I got totally confused. Can someone either tell me what I need to do or give me a link to instructions?