How to setup DNS on Ubuntu 18.04

Having wasted a lot of time on my last install most likely because of some faulty DNS setup I hope to do it right this time. However, I am totally lost when it comes to the Virtualmin settings.

During the setup Virtualmin asks “For DNS zones created by Virtualmin to be resolvable, the primary nameserver record for each zone must be set to something that can itself be resolved by other systems on the Internet. Primary nameserver:”.

My hostname is just a random name so it doesn’t work. So I took one of my work domain names that I want to host on the server in the future. But this raises the obvious question what should happen if I might direct that domain name to another server in the future. Should I use instead the Digitalocean name servers?