Intuition is organized as a library of over 100 functions.  Before using
an Intuition function you must first open the Intuition library.  (In
general, you must always open a library before you can call the functions
of that library.  See Chapter 1, "Introduction to Amiga System Libraries".)

 Components of Intuition 
 Screens and Windows 
 Gadgets, Menus and Requesters