Example:

Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);

Shape shape = builder.insertChart(ChartType.LINE, 450.0, 250.0);
Chart chart = shape.getChart();
ChartSeriesCollection series = chart.getSeries();

// Delete default generated series.
series.clear();

String[] categories = new String[] { "Category 1", "Category 2", "Category 3" };
series.add("Series 1 of primary series group", categories, new double[] { 2.0, 3.0, 4.0 });
series.add("Series 2 of primary series group", categories, new double[] { 5.0, 2.0, 3.0 });

// Create an additional series group, also of the line type.
ChartSeriesGroup newSeriesGroup = chart.getSeriesGroups().add(ChartSeriesType.LINE);
// Specify the use of secondary axes for the new series group.
newSeriesGroup.setAxisGroup(AxisGroup.SECONDARY);
// Hide the secondary X axis.
newSeriesGroup.getAxisX().setHidden(true);
// Define title of the secondary Y axis.
newSeriesGroup.getAxisY().getTitle().setShow(true);
newSeriesGroup.getAxisY().getTitle().setText("Secondary Y axis");

// Add a series to the new series group.
ChartSeries series3 =
        newSeriesGroup.getSeries().add("Series of secondary series group", categories, new double[] { 13.0, 11.0, 16.0 });
series3.getFormat().getStroke().setWeight(3.5);

doc.save(getArtifactsDir() + "Charts.SecondaryAxis.docx");