What is a domain?
A domain can represent your name or your project on the Internet and make it accessible worldwide. You can use a domain for example to make a website reachable online, furthermore you can forward a domain to a game or TeamSpeak 3 server and reach it online with an easy memorable name.
A subdomain is a child domain which you can create at any time for free for your existing domain. This is done via the DNS settings, a subdomain can look like this for example: server.fivem-server.com.
In this case server is your subdomain and fivem-server.de is the name of the actual domain. A subdomain usually redirects to a different address compared to the actual domain, so you can for example make your website accessible with fivem-server.com while you can connect to your FiveM or another game server with server.fivem-server.com.
Domains and IP addresses
Unlike an IP address, you have to rent a domain individually, this is NOT automatically included with a game server, root server, VPS or voice server. A domain already differs in appearance from an IP address. While an IP address consists of numbers, for example 22.214.171.124, a domain has a real name and a corresponding domain extension, for example fivem.net. So fivem would be the name of the domain and .net the domain extension. Besides .net there are of course many other domain extensions like .com or .de.
Find out how to rent a domain here: Order a domain