Do this first, before you set up the computers that your phoners will use. That way, as you are setting up the phoners' computers, you will be able to look at the admin screen to verify that your phoner computers are being logged in correctly.
Your welcome email will include a link to the login page for the admin system.  Go to your browser (any browser will work).  Click on the link in your welcome email - or type the address into the browser.  Bookmark the login page.
You can now log in with your admin or supervisor username and password.