This tool draws regions with straight edges. It is deprecated in favor of the Spline Tool which can draw straight edged polygons and also curved shapes.
Here are some example polygons (in case you forgot what they look like):
Note that the edges can cross each other. When they do, the Winding Style Parameter comes into play.
The Tool Options Panel allows you to specify:
Name : Used for the new layer; any number in this field will automatically increment with each layer created
Blend Method Parameter : The blending method used to composite on the layers below
Opacity : Sets the Opacity for new layers. Defaults to 1.00 (Completely opaque)
Invert : Whether invert the create(d) layer(s). Is related to his Invert Parameter.
Link Origins : Whether Link the Offset of Splines
Just click over the different corners of the polygon.
To finish the creation of the spline you have different options :
Click again over the first vertex.
Using the gear
Make Polygonbutton at the bottom of the Tool Options Panel.
Select any other tool from the Toolbox Panel.
Clear Current Polygon button at the bottom of the
Tool Options Panel could be used to clear the current polygon.