Click the "Sign up" button to be taken through a process to add your Organization (Fire Department, Police Department, Business, School, College, etc.). And you will be the initial "Organization Administrator" -- or "Org Admin" for short.
You will be asked to use a unique, short, memorable "prefix" to call your own (called a subdomain, in technical terms). Your organization may lend itself well to an abbreviation, or your organization's email and/or website may already have a simple domain name that you should use.
For example:
Upper Makefield Fire Company ==> umfc
Bethlehem Fire Department ==> bfd
Enter your organization's main street address, as it will show up on the map view in Blazemark.