Custom Hostname! How?

You would need Domain Registration for your own domain name and DynDNS Standard DNS as the DNS hosting service for this domain.

Edit:

do I first create a domain ex: "domain.com" and can then create my custom hostname ex: "domain.server.com" that points to a ip-adress?

This what you call "domain.com" (better: http://example.com) is your custom hostname already which can point to any IP address. Even more, you can then create subdomain names like http://john.example.com or http://paul.example.com or http://marie.antoinette.example.com which again can point to the same or another IP address or can be an MX record or webhop or what else, as needed and as you want.

No, you purchase domain registration and Standard DNS for example.com. Then you create server.example.com in that domain, that points to an IP address.

I am a beginner with all this, so do I first create a domain ex: "domain.com" and can then create my custom hostname ex: "domain.server.com" that points to a ip-adress?

Again thanks!