In order to become or work as a property manager the property manager will be required to have either a property management license or a Real Estate broker's license in order to conduct any Real Estate transactions legally.
That license includes anything related to Leasing and Managing Rental properties.
There's a couple states however that don't require the licenses to be a property manager so check with your state to be sure on the laws before you become a property manager.
Another thing you need to become a property manager is a Bachelors or Masters Degree in Real Estate and Property Management.