Before the polygon is started the line width and color can be set. The PolyGon Line Width field is a scaled dimension in inches if >0. If 0 it is a 1 pixel wide line at all zooms. If the value is negative, it is a scale-independent number of pixels wide.

Polygons are created by either a series for Left-Clicks or Left+Drags, and a new "node" is placed for each. When using Left-drag, the node will be positioned when you release the button.

If MagneticSnap (Magnetic Snap) is enabled, An anchor point will be shown on nearby draw objects that the next point will be snapped to unless Alt is held.
If it is disabled, the snap will only occur if Alt is held.
If Ctrl is held down when a new point is placed, it will snap the relative angle of the new side to a multiple of 90 degrees from the previous side. On the first polygon side this will be at a multiple of 90 degrees to the axes. The line from the previous point will be highlighted in Blue.
A special blue square anchor will show when the cursor is in a position such that it is 90 degrees away from both the last point and the first point of the Polygon.
The last polygon segment dimensions can be altered using the text boxes that appear showing the segment length and the relative angle to the previous segment.
A polygon is closed if the next node is place over the start of the polygon
The polygon is ended using Enter or Space. The polygon will be auto-closed.