Users

• Some computer programs execute without user interaction. However, many applications, such as word processing programs, Web browsers and operating systems, respond to user interaction, giving the computer user a level of control over the processing being carried out. In this model, when a program first executes, it carries out setup tasks, then presents user controls and waits for user interaction. When the user interacts with the application, it will carry out programming processing according to this interaction. For example, if you click a bookmark within your Web browser program, it will carry out the processing necessary to fetch the requested Web page and present it to you.
  
  

Application Processes

• Computer programs typically define various different processes. Programs in languages such as Java sometimes define these processes as methods, also known as functions. This is one of many ways in which programs divide up the various tasks associated with an application, calling on these distinct sections of processing when necessary, for example fetching a Web page in the case of the browser program. When programmers create applications they therefore define the processes that are possible, but in many cases these processes will only execute if the user requests them to through the Graphical User Interface.
  
  

Controls

• GUI applications can involve a variety of user controls. Web applications operate through the Web browser and can include HTML user controls such as buttons, check-boxes, drop-down lists and text-areas. Software applications running on a desktop or laptop PC can also include similar user controls such as push buttons, radio buttons, text-fields and menus. The controls within an application are designed to allow users to carry out specific tasks. For example, in a Web application in which the user needs to enter her name, the user controls will likely include some sort of text input element.
  
  

Design

• User interface design is a specific area of computing expertise in its own right. When designers construct GUIs, they create the user controls necessary for application processing, then combine these into a visual design. Typically, Graphical User Interfaces go through stages of testing, not only to ensure that they work, but also to measure how successfully they allow users to carry out the necessary tasks. Designing a user interface that people find intuitive to interact with often requires a high level of skill, particularly with complex applications.