Here is a quick description of each of theicons on the top left side. The best way to learn what they do is to try them out. Remember that the panel in the top right corner will always tell you what the mouse buttons do, and that a right-click will always quit out of the current operation.
Draw a circle by defining the center and a point on the circle.
Draw a circle by defining two ends of a diameter.
Draw an ellipse by defining the center and one corner of the bounding box.
Draw an ellipse by defining two corners of the bounding box.
Draw a closed curve by defining the enclosing polygon.
Draw a free curve that fits a polyline.
Draw a closed curve by defining points on the curve.
Draw a free curve passing through a set of points.
Draw an arbitrary polygon.
Draw a polyline, that is, a series of line segments connected end-to-end. A single line segment is just a polyline with only two points.
Draw a rectangle by defining two opposite corners.
Draw an oval inscribed in a rectangle.
Draw a regular polygon.
Draw a circular arc defined by three points.
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Add textual annotation (large letter T).