Before drawing or writing on the screen each program which is using the server creates one or more windows. The windows exist in a tree structure growing down from the RootWindow which covers the whole display.
Many applications only use windows which have root as the parent.
No window appears on the display until it is mapped, all its ancestors are mapped and an expose event has been received. Furthermore the mapping command must reach the server before anything will happen. The subroutines for mapping windows are given later in this section. Creating a window alone is not sufficient to enable you to actually see anything on the display. If you don't want to bother setting up too many things, you can create windows that inherit their attributes from their parent.