Suppose you have a visual part named DirectoryView, for which
you want to add the following user interface:

To define this user interface, first, add a push button to the empty window in the Composition Editor:
(Buttons category) and
(Push Button part) from the parts palette. After you select them, the
status line along the bottom of the editor shows: Category:
Buttons Part: Push Button

Next, add the other parts. You'll need:
category
part
category
part
After you add the parts, the window resembles:

"Example: Change a part's settings" explains how to change the parts' settings.