Intuition also supplies a menu system for accepting commands and options
from the user.  A menu is a list of choices displayed at the top of the
screen from which the user can select with the mouse.  Each screen has one
menu bar that all application windows operating on the screen share.
Whichever window is active controls what appears in the menu bar.

     Figure 2-4: An Intuition Menu 

The current set of menu choices can always be brought into view by
pressing the right mouse button (the menu button) thus providing the user
with a familiar landmark even in unfamiliar applications.  Menus allow the
user to browse through the possible set of actions that can be performed
giving an outline-like overview of the functions offered by a program.

Menus are discussed in detail in Chapter 6, "Intuition Menus".  Additional
information on programming menus for Release 2 of the operating system can
be found in Chapter 15, "GadTools Library".