This widget is a horizontal spinner. Excepts its look (the buttons are located on both side of the text area), it has the same behaviour and methods than the Spinner widget.
Use it like the Spinner widget.
An example called HorizontalSpinnerSnippet.java is located in the plugin org.eclipse.nebula.widgets.opal.horizontalspinner.snippets.
This example is also available here : HorizontalSpinnerSnippet.java