First, open your web browser and go to https://corr.maps.arcgis.com then click the 'CORR' button under Enterprise login:
After that, you will be prompted to sign in to your organization account with the city. It will be your city email address for the username and your regular password you use to login to your city computer. That screen looks like this:
Once you sign in through your organization account, you will automatically be redirected and signed in to the City of Round Rock's ArcGIS online site:
Congratulations, you now have a CORR ArcGIS Online account!