Icons in the panel window represent object manipulation functions,
modes and other drawing or modification aids.
Manipulation functions are selected by positioning the cursor over it and
clicking the left mouse button. The selected icon is highlighted, and
a message describing its function appears in the message window.
The left and middle buttons are used to create and modify objects in the canvas
window. Most actions start with clicking of the left button
and end with clicking of the right button.
There is no need to hold down a button while positioning
the cursor.