Shapes can be Lines, Ellipses, Rectangles or Arrows. New shapes are drawn via the Tools|Drawing tools menu (or Selection menu|Add objects). Click left to place upper left corner then click left to place bottom right corner. Shapes are resizable via the two corner markers. Press Ctrl to force squares and circles.
The input dialog for Rectangles and Ellipses allows setting of brush color with a filling pattern including gradient fill. For Arrows the arrow styles for start and end is selectable.