The term "window" is very broad and includes simple windows, push buttons, dialog boxes, list boxes, combo boxes, scroll bars, buttons, static text, group boxes, checkboxes, and radio buttons. Using these elementary units, you can build up complex GUIs. Each window maintains a parent-child relationship with the windows that are placed on it. The way you program GUIs is modeled after how they are displayed, you create each individual sub-window and set up the parent-child relationships.

Each time a window is created, you must specify the parent that "owns" the window. You must also specify a "name" so that the new window may be referenced by other instructions. Most other commands use this name to identify the Window or control you wish to communicate with. When a parent window is deleted, its "child" Windows and controls are also deleted.

When controls are in windows, the coordinates used by all the Windows procedures are in Windows coordinate system (not the turtle coordinate system). That is the Y axis is upside down (positive numbers are down). Likewise, the origin is not the middle of the screen, it is the upper left hand corner of the window. Furthermore, the position and size are given in "dialog units", which are proportional to the size of the font that is being used. This ensures that the dialog boxes have a consistent layout, regardless of the font size.

When controls are on the FMSLogo screen window the coordinates are in the turtle coordinate system.