Classes in the System.Windows.Forms namespace are used to create rich-client applications using C#. The Form class is the base class for most windows in a Windows Forms application. When you add a new form to your Visual C# project, the class will be created with a number of necessary methods already defined. The Form class exposes a number of properties that can be changed programmatically or through the Forms Designer’s Properties window.
The MessageBox class is used to display message boxes to users and includes a wide variety of options that control the appearance of the message box. Using the MessageBox class, you can control the display of icons, button placement, and other properties.
A Windows Forms application is controlled by the Application class, which is responsible for starting the application’s message loop and displaying the top-level window. The Application class also includes properties that calculate the proper locations for storing per-user or application data. Instead of creating an instance of the Application class, you call static methods exposed by the class, such as Application.Run and Application.Exit. You can also use form properties to control form behaviors such as setting a form’s border style and defining its background color.