The Create Polygon Tool lets you draw arbitrary polygons. To start, click on the spot where you want the first point to be located, then click again on the spot where you would like to put the next point, and so on. To finish creating the polygon, either double-click when creating the last point, press the "Finish" button on the toolbar, or simply switch to a different tool.

Finish: Pressing this button finishes creating the current polygon.