The ISPConfig hosting control panel is on port 8080, so if your web site is example.com, ISPConfig is at https://example.com:8080
Unfortunately, unless you have installed an SSL certificate for your site, your web browser will get sent our SSL certificate, and the browser will complain that the name of the site you visited (example.com) doesn't match the certificate presented by the web server (*.elirion.net). You may be able to tell the browser that this is what you expected and to go ahead and show you the site. Otherwise, unless you've been told that this will not work, try visiting https://www.elirion.net:8443/ instead as your web site is likely to be on the same hosting server as the main elirion web site. (If you're on a different server, you'll need to use something like https://bigbird.elirion.net/)
If you get a warning about SSL, try https://linnet.elirion.net:8080 instead.
You can log in using the user name and password from your welcome email. If you don't know your user name, try the "password lost" button.