Virtualmin Post-Installation Wizard is straight forward during your first sign-in. In this post, this will be a quick tour of how the wizard works.
However, if you have not created your first Virtualmin installation, you may refer to Install Virtualmin in Ubuntu 16.04 post.
For MySQL password, I usually leave it by default, then just copy the password for use.
If you wish to create your own name servers, just like I have shown above, visit this article Setup own name server in Virtualmin
If you have successfully completed the Post Installation. You should be all set to get to the Virtualmin Dashboard as shown below: