Typically, you’ll want to use your Accelerator to serve websites and handle mail with your domain(s). A domain is typically understood as a hostname of two parts (e.g. mydomain.com), sometimes of three parts (e.g. mycompany.co.uk) - compared to subdomains which usually introduce an additional minor part (e.g. blog.mydomain.com).
You can use Virtualmin to manage domains through the Virtual Server feature.