The plug-in comes with three built-in shapes: "Line", "Circle", "Semi-Circle". When setting the page item value, you can set both the percentage and (optionally) the text using a colon separated value e.g. {Percentage}:{Text}
Using Javascript you can set the value dynamically using the apex.item API e.g.
// Set the progress %
apex.item('P1_ITEM_NAME').setValue(75);
// Set the progress % and the message
apex.item('P1_ITEM_NAME').setValue('75:Loading...');
Custom Shape
You can even include your own custom SVG shape to show progress.