This only applies to the Advanced, Professional and Enterprise level plans.
If you are on the Starter or Standard plans, there are no additional users except the account owner as these plans to not include multi user access.
There are 3 different access levels in Pingdom, this is selected when a user is invited and can be edited later by an admin or the owner
The current options available are:
Can make changes to the account, checks, etc. Including changing subscription information, invite new users and much more. Change alerting settings for checks, users and contacts
Can add and edit checks, users and contacts as well as view reports.
Can view checks, reports and outages.