A Realtor is a licensed Real estate Sales Agent who is a member of the National Association of Realtors.
A Real Estate Agent is the same as the Realtor with the exception that they are not a member of the National Association of Realtors.
A Broker is the one responsible for supervision and inspection of the conduct and or transactions for the Agents/Realtors under their care. Essentially, they are the responsible party as the agent acts thru them to conduct business.
The Difference in Plain language is that a Realtor has a typically higher code of ethics to answer for though the National Association of Realtors since they are required to take additional training. Both sales agents and brokers can be Members of the Nation Association of realtors