You can log in to Plesk by visiting the following URL:
https://<Plesk server's address>:8443
where <Plesk server’s address> is either the domain name or the IP address of the Plesk server. Type in your username and password to log in. When you are logging in to Plesk for the first time, the scenarios will differ depending on whether you are a shared hosting customer, or an administrator managing your server.
NOTE: You would have received the username and password in a welcome email when your account was purchased.