If your hosting package includes more than one domain name (website), then you can easily add domains to the server. Before you start adding a new domain that will use a second-level domain name, like example.com, be sure to register this domain name. If your hosting provider provides the domain name registration service, you can do this from the Customer Panel as described below. Otherwise, you should register your domain name with another domain name registration authority.
You can set up the following types of site configurations through Plesk:
> Website addressed by a second-level domain name. The following services are available for websites:
> Website or a division of a website addressed by a third-level domain name (subdomain). This is usually a division of an existing site. It has an Internet address comprising of three parts separated by dots. The following services are available for subdomains: