California has a Residential Real Estate Brokerage System.
440,000 Licensed Professionals  assist with the purchase and sale of Real Estate.
120,000 are Brokers and 320,000 are Agents that must work for a
Broker to participate in the system. 

Brokers are individuals who are at the top of the Brokerage System.
They are the people allowed to "Broker" Deals. 
They are responsible for Listing Properties for Sellers.
The are also  responsible for representing Sellers and Buyers
in transactions via "Agency" agreements. 

Brokers can act as the Agent for their Clients OR
they can "employ" Agents to do representation under their Supervision.