In other words, the data in a class can be hidden from the rest of the program and access to that data limited to the functions you add to the class. Start attaching code to various events. Place additional functions in the declaration section of forms or modules, depending on whether they are shared among forms or by programmer's whim. Define variables and otherwise write the program. Define the classes the application will use.
Classes correspond to key data structures or areas of functionality.
Classes may be made up of other classes. Now go ahead and draw the form and implement the program. Design always comes first. Taking the time to design your application is the single most important thing you can do to improve the quality of your code, reduce its size, increase its reliability, and accelerate its performance. And implementing your application as a collection of classes will make your programs even better.