When you use the "NetBeans Platform Application" template in
NetBeans IDE and you make no changes of any kind, simply run it,
you'll find that your "File" menu has this content, by default:
Let's now imagine we want to add an "Open File" menu item to the
"File" menu that you see above. Of course, you could create that
menu item and the related GUI and functionality yourself.
Or, you could reuse the functionality from NetBeans IDE, which
comes from a module named "User...