A window or frame is a user interface element, which is used to organize information in an application. The information in a window consists of objects (and their properties) that enable users to perform actions or to report information about actions.
Primary windows, secondary windows, utility windows, and plain windows provide the top-level containers for your application.
A primary window is a window in which the user's main interaction with the data or document takes place.
A secondary window is a supportive window that is dependent on a primary window (or another secondary window).
A utility window is a window whose contents affect an active primary window. Unlike secondary windows, utility windows remain open when primary windows are closed or minimized. An example of a utility window is a tool palette that is used to select a graphic tool. A plain window is a window with no title bar or window controls, typically used for splash screens.
Besides this, there are other user interface components like buttons, combo boxes, list boxes, text area etc. We will be discussing these after discussing primary window in detail.