How is real estate broker differ from real estate agent?

This varies by state. Some states have broker licenses as well as real estate salesman's licenses. Other states have gone to a brokers license only situation. A broker usually has the right to open an independent real estate office and in the past had more experience than an agent with just a salesperson's license. The educational requirements were also more extensive.

Many people referred to all agents as "brokers" but that is usually incorrect. This response is addressing residential real estate as practiced in the US only.