To open the Freehand tool, double-click on "Freehand" in
the Toolbox. While Freehand is the Current Tool, you can LMB drag in any Camera view:

As soon as you release the LMB,
the tool creates a polygon identical to the shape you drew:

Note that the polygon that is created is exactly the same shape and
aspect ratio as the shape you drew, but it is part of the plane defined by the two axes
that arent currently Active (the XY
axis in this example, since the Z axis was Active
when the shape was drawn) centered at the origin. The tool will display the number of
points in the polygon you create.
If youre unsatisfied with the shape of the polygon you create,
simply LMB drag the mouse again, and the polygon
will be replaced by the new shape. At any time you can:
Hit the OK button to close the Freehand tool and keep the last
polygon;
Hit the Cancel button to close the Freehand tool, discarding the
last polygon;
Hit the Create button to make the last polygon
"permanent", and reset the counter so you can continue to create freehand
polygons.