After you purchase a domain, its registration can require some time. The reason for the delay is that name servers update their zone information periodically. Thus, until all name servers have received information about your zone, you will not be able to access your site by its domain name. Nevertheless, you can always access your site during domain name propagation using the Preview button on the Websites & Domains tab.
During domain name propagation other people can access your site too. For this purpose, Plesk registers your website as a subdomain of one of the provider's sites. For example, if your website is my-domain.tld and a provider has configured the preview service on provider-domain.tld, you can access your site on my-domain.tld.192-0-2-12.provider-domain.tld. Here 192-0-2-12 is the site's IP address where dots are replaced with dashes.
