Use the Draw Face button from the Create palette to draw a 2D face:
You can draw on top of an existing object by clicking the Draw Face button, then click on the object to begin drawing.
The Draw Face tool is a bezier pen. Click to create an initial point, then move the cursor to position a second point and click to create a straight line. Dragging creates a center point around which you can bend the line between two points.
Click-middle to close-off and finish the shape.
Jump to: Creating Basic Shapes and Text