Upon completion of your Plesk installation, your Plesk login URL will be using the following 2 options for you to access to the control panel:
The server hostname depend really on the providers you are using. If you are on some hyper-scaler cloud hosting provider, some would have generate a generic hostname using their own hostname for you to use. You can however set a different hostname for your Plesk server as well. Find out details from their support documentation on how to do this.
If you run your Plesk on the conventional dedicated server or VPS environment, most providers allow you to setup and configure your own hostname. Make sure this hostname can be resolve/ping with the right IP return as your Plesk server IP.