You can log into plesk by going to https://domain:8443 or https://ip:8443 Where domain is your website, ip is the address to your server; you can get your ipadress by contacting tech support. Using the ip adress will allow you to manage your account even before the domain is active

Plesk is commercial web hosting data center automation software developed for Linux- and Windows-based commercial hosting service providers. Plesk was designed to install and manage web hosting systems and applications on a single server. The control panel is designed to simplify the management and administration of the web sites by automating various tasks on a single server.