A control is a predefined child window that carries out a specific kind of input or output. For example, to make your application retrieve a filename from the user, you can create and display an edit control in which the user types the filename. An edit control is a window that receives and displays keyboard input.
A control, like any other window, belongs to a window class. The window class defines both the control's window procedure and its default attributes. The window procedure is important because it determines the appearance of the control and how it will respond to user input. Window procedures for controls are predefined in Windows, so no extra coding is required in your application when you use a control.