The document describes Pure Data's object-oriented programming model, where all elements like boxes, objects, classes and inlets/outlets are represented as objects, with classes defining common behaviors and properties of objects, and objects being instances of classes that can receive and send messages through inlets and outlets. Key elements include the class struct that defines methods like initialization and message handling, the t_object base class, and fundamental data types like symbols, atoms, and inlet/outlet objects that allow communication between objects.