1) Object-oriented programming (OOP) uses classes and objects to organize code and data to make it more modular and reusable. Many popular languages like Java, C++, and C# use OOP. 2) A class defines the data (properties) and behavior (methods) of an object. Constructors are used to create objects from classes. 3) To access data and methods of an object, it must first be instantiated by using the new keyword followed by the class name, then its methods and properties can be called.