To use your own domain on a server rented by us, you don't need our nameservers.

To set up the domain on the server, you have to change the "A-Record" in the DNS zone of the domain and if necessary the "MX-Record" to the IP of the rented server.
The MX-record may also be the domain itself, e.g. xyz.de (without IP of the server), for this the mail server would have to run on the same server accordingly.

Some domain providers don't provide you to access the DNS zone, in this case you should contact the support of the domain provider.
If it is not possible to change the IP, you can either move your domain to us or host your own name servers on the server (free of charge). Prerequisites for your own nameserver can be found in our FAQ, in this article.

After you have changed the A-record to the IP of the server, you can set up the web server (e.g. Apache2) on your server or the domain via the admin tool (e.g. Plesk or cPanel) accordingly.