Consider an automobile :
You add gasoline into the tank.
You turn the key in the ignition.
You engage the transmission to indicate the direction of motion.
You press the accelerator to initiate motion, and adjust speed.
You use the steering wheel to guide motion.
You press the brake to reduce speed.
You can do all of these activities without ever looking under the hood !!
A programming object is similarly accessed as a black box, via its methods.
Programs that interact with an object, are shielded from how information is stored by the class.
The class implementation can use alternative techniques for storing the associated information, provided that the methods behave as expected.
Object methods can provide the illusion that information is directly available, hiding the actual location and representation of the information.