Use the XtAddCallback() function as follows:
XtAddCallback ( Widget widget, String DtNhelpCallback, XtCallbackProc HelpRequestCB, XtPointer clientData );
The widget where you want to activate the help key.
The function in your application that handles the help request when the user presses the help key.
The data you want passed to the HelpRequestCB() function. Typically, this data identifies the topic to be displayed.
When the user presses the help key, the help callback is invoked for the widget with the current keyboard focus. If that widget does not have a help callback, the help callback for its nearest ancestor that does have a help callback is invoked.
If no help callbacks are found, nothing happens. Therefore, it is recommended that you add a help callback to each shell in your application. This ensures that no user requests for help are lost.
Adding a help callback to a dialog shell automatically enables the Help button on the dialog to invoke the help callback.