Most states require real estate sales professionals to be licensed by the state, so that they can control education and experience requirements and have a central authority to resolve consumer problems.
The terminology used to identify real estate professionals varies a little from state to state. Brokers are generally required to have more education and experience than real estate salespersons or agents.
The person you normally deal with is a real estate agent or salesperson. The salesperson is licensed by the state, but must work for a broker. All listings are placed in the broker's name, not the salesperson's.
A broker can deal directly with home buyers and sellers, or can have a staff of salespersons or agents working for him or her.