Step 2 - Application Classes
If you are here for the first time, just create the application classes (that you know of already), define their methods and make them compilable. You can do more, but if you prefer "test first" you don't do that now. ("test first" means, you synchronize with your tests first, implement them, see them failing... not before then you start to implement the application classes and make them pass the tests.) For now let's compile the application classes.
If you are here for the second time, chances are some tests have failed. Implement and run the tests again. If you need to create a new class or a public method, don't forget to synchronize your tests (see above).