Add subdomain to Minecraft server?

I want to set up a Minecraft server under Ubuntu. I already know how to do that. But now I wanted to know how I can set up my own subdomain on the server. How does it work?

So you can use no-ip, for example, which is a free domain service and the only thing you have to do to make your minecraft server accessible is that you first have to release ports on the Fritz box for the ubuntu computer and then on the computer Install the update program from no-ip.

there are enough tutorials on YouTube