Using classes in Java involves calling methods and accessing fields on objects. Using dot notation 'object.method()' or 'object.field', you interact with object instances. Methods perform operations, while fields store data. Proper class usage respects encapsulation—accessing fields directly is often discouraged in favor of methods (getters/setters). Understanding how to use classes correctly is essential for object-oriented programming and enables you to work with both your own classes and Java's extensive class library.

Mastering class usage enables you to leverage object-oriented design effectively. Being able to call methods and work with object state is fundamental to using APIs, frameworks, and libraries. In professional development, class usage appears constantly: calling methods on collections, using streams, working with file objects, and interacting with frameworks. For example, 'list.add(item);' uses a List object, while 'file.read();' uses a File object. Understanding instance versus static members is crucial.

By learning class usage thoroughly, you'll be able to work with Java's rich ecosystem and design your own intuitive APIs. Understanding encapsulation and proper field access (use methods, not direct field access) prevents coupling and enables maintainability. This skill is essential for professional Java development. Prerequisites include understanding class basics, methods, and objects in Java.