When a person first becomes licensed to become a real estate agent, he/she obtains a real estate salesperson's license (or some states use the alternative term, "broker") from the state in which he/she will practice. If you want to obtain a real estate license, the candidate must take specific coursework (of between 40 and 90 hours) and then pass a state exam on real estate law and practice. In order to work, salespersons must then be associated with (and act under the authority of) a real estate broker.
Many states also have reciprocal agreements with other states, allowing a licensed individual from a qualified state to take the second state's exam without completing the course requirements, or, in some cases, take only a state law exam.