network settings Ubuntu

All required Information is in the SCP, as well for IPv4 as for IPv6.

Nevertheless, DHCPv4 should work, even if not recommended.

That is a quirky configuration. The subnet is supposed to be in CIDR format, like the way your address is given in the server control panel. Basically the same as the address, but with the netmask length, like 192.168.0.1/24 if your address is 192.168.0.1 and your netmask is 24 bits. Actually you're supposed to clear the bits that identify the host in the subnet, but it should work if you just put the CIDR address there. The address is the same without the netmask. The gateway is given in the SCP. The nameservers aren't specified anywhere, but there is a topic in this forum. You can use any nameservers you like, for example 9.9.9.9 (Quad9), 1.1.1.1 (Cloudflare), 8.8.8.8 (Google), etc.. You can leave the search domain empty. That's a list of domain suffixes that the resolver should try adding to hostnames without a dot. This is rarely used.

In case of network trouble, the rescue system can be a reference for checking if the virtual machine is working correctly.

This gets you all the parameters from the address as given in the SCP:

http://https//mxtoolbox.com/SubnetCalculator.aspx

Enter just the address, select the netmask length from the dropdown menu and click 'calculate'.

(Canonical really needs to overhaul that configuration form. That's archaic.)

Please, make yourself familiar with basic knowledge about IP networking. And I mean really just the very basic knowledge.

How will you manage your server when it comes to Firewall and security settings? Be aware that your server is attacked once per second as soon as it has a public IP address. And there is no system firewall at Netcup, like other hosters do it. You have to configure everything on your own. Are you sure, you are able doing this?

Oh no, by failing to guess the unusual network configuration format that the Ubuntu installer expects and not being able to do bitmask calculations in your head you have triggered the only-senior-admins-can-run-servers reflex of frank_m ...

Nonsense.

But everything, that is currently required, is written down in #2. As soon as he gets familiar with IP networks, he can configure his server. He will need it anyway. If not today, latest tomorrow.