The following explanation applies to all charts, not just the Gantt Chart.

• Click and drag the mouse inside the diagram (the dark gray area) to define the date range you want to see (horizontal zoom in).
• To view the whole date range again, right-click inside the diagram und select "Auto Range -> Range Axis".
• Right-click -> "Print" prints the diagram directly.
• Right-click -> "Properties" let you change almost everything, e.g. the used font or color.

The following image shows the same chart as above but zoom in to the project duration: