- OOP programs model real-world entities as interacting objects. A class defines the common properties and behaviors of objects, while objects are instances of a class. - The document discusses key concepts in OOP like classes, objects, fields, constructors, methods, encapsulation, inheritance. It provides examples from the GridWorld framework to illustrate these concepts. - The last section reviews the key points about classes, objects, fields, constructors, methods, access modifiers, and inheritance.