Master Logins are the administrative logins that allow the user full access to billing and account holder information as well as all features and settings for all numbers assigned to the account.
Toll Free Number Logins have full access to the features and settings for the 800 numbers assigned to their login, but cannot view the billing or account holder information.
Ring-To Number Logins only allow the user to view the Call Detail for calls to the toll free number that rang to the specific locations (ring-to numbers) assigned to the login. Especially helpful if you have multiple users in different locatioins sharing the same toll free number.