- Objects are represented by their properties and methods, and are instances of classes. A class defines a set of objects. - In PowerBuilder, classes are defined using painters like the Application, Menu, User Object, and Window painters. Class definitions are stored in libraries like PBLs, PBDs, DLLs and EXEs. - Properties and methods can be added to classes. Properties are added as instance variables, while methods include events, functions, and external functions. Common types of methods that can be added are events, object functions, and external functions.