A real estate agent is someone who is licensed to help you buy or sell a home. The agent will earn a percentage commission on the sale, usually paid for by the seller. A real estate agent is not licensed to work independently, however, and must be employed by a real estate broker.
A real estate broker can also help you buy or sell a home, but they are licensed to operate independently as well as to employ agents on their team. Any agent working for a broker (whether a larger firm or a small, independent brokerage) will have to split part of their commission with the broker.