The two have some differences:
Mechanically - A Continuous Rotation Micro Servo is a servo motor without the angle limits, it is free to spin continuously. The servo 9g, on the other hand can go from 0-180 degrees. it has mechanical limits to its rotation.
Functionality - the continuous motor is usually used more like a regular motor, for driving wheels or gears, where the other one is used for angular tasks - opening a door or turning a sensor a to a specific direction.
coding - the code interface of both motors is the same. Use the IDE built-in Servo library to send them commands using servo.write(arg);
the ‘arg’ in each case has a different meaning: in the case of the servo 9g - this determines the desired angle where for the continuous servo it will determine the speed. for more information, add them to your circuit and brows the code comments.