On this page for company settings you can adjust assignment order of the new jobs. By default this will be set to Default carrier. Which means all new jobs will go to a default carrier.
You can also choose if the company should assign jobs to one carrier (default one) or shares with other carriers.
Company availability
Scenario for summary of availability when sharing with other carriers:
Company has a default carrier "Carrier 1"
Company also uses "Carrier 2" and "Carrier 3" for their pool of availability