This demonstrates one way to set up and use Motif pulldown menus.

There are two menus, File and Edit.
The File menu has several items, including a separator line,
and keyboard accelerators for the menu items.
The Edit menu also has several items, but rather than simple push
button items, this menu has a toggle button and three radio buttons.

Menus can be in the popup planes or the normal planes.
When in the popup planes, they show and hide without forcing
a redraw of the entire scene. However, they are limited in the
number of colors they can have. For instance, toggle buttons on
menus in the normal planes can be colored yellow for easy visiblity,
but in the popup planes have no color, and are more difficult to see.
When there is a complicated scene, though, it is best to have the
menus in the popup planes. (All viewers put menus in the popup planes.)

The src file has a #define MENUS_IN_POPUP which forces the menus
into the popup planes. Removing this causes the menus to appear in
the normal planes.
