There are some good examples in this sample: Add graphics | ArcGIS for Developers
Create Points, using geographic coordinates for example, as follows:
// points
Point point1 = new Point(13, 55.59);
Point point2 = new Point(72.83, 18.97);
Point point3 = new Point(5.43, 34.3);
The way to create a Polyline is as follows...
Polyline polyline = new Polyline();
polyline.startPath(118.169, 34.016);
polyline.lineTo(104.941, 39.7072);
polyline.lineTo(96.724, 32.732);
...and a Polygon:
Polygon polygon = new Polygon();
polygon.startPath(25, 5.59);
polygon.lineTo(13.42, 3.92);
polygon.lineTo(12.3, 23.3);
polygon.lineTo(38.2, 22.9);
polygon.closePathWithLine();