Business objects are described through class descriptions. For example, in an object model for a University you might describe: a Student class, a Faculty class, a Course class, a Schedule class, and so on.
Describing a class with the Model Browser is similar to defining a class in a Smalltalk browser. Each class consists of attributes (instance variables) and relationships. Attributes typically describe the granularity of the objects you wish to persist. Relationships describe how objects in your model are associated with one another. In the University model, your Student and Faculty classes might have attributes such as studentNumber and facultyNumber, respectively. In addition, there might be a relationship between the two classes, a relationship between Faculty and Student, for example. A Faculty object, for example, could have an advisedStudents relationship, or role, with several Student objects.
There is a difference between describing a class in the Model Browser and defining a class using other tools. Describing a class does not create an instance of the class. It creates metadata for the class. The metadata is used later to generate the class instance. The instance of the class is created when you use the Generate function under the Models menu. Generating the code for your model is typically done after you have described all the classes. If you need to make changes to your model after you have generated the code, you need to generate the code again.