How to create the hostname?

[whatwhat0x]

Hello, i have a newbie question. I am sorry.
I used the docker container.
But i dont know how to set the hostname.
Like this:

right now my hostname is not my domain, but my provider name.
it's random like: 4034384-934959-ooo-provider.net
how can i set it with a better name?
like: dns.mydomain.net

and what are the benefits of doing this?

thank you very much.

here is another one to show you what i mean:

[encrypt.town]

It's the rDNS, you have to ask your server provider to set it for you :)

[whatwhat0x]

thank u that solved it

[Frank Denis]

Just curious: what are these screenshots from? What software is that?

[mibere]

The first one looks like https://dnsleaktest.com/ and the second is the table from https://dnscrypt.nl/