begin
  DrawPolygonRegion(Panel1.Handle, Panel1.BoundsRect, SpinEdit1.Value, False);
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
  DrawRndRectRegion(Form1.Handle, Form1.ClientRect);
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
  DrawPolygonRegion(Panel1.Handle, Panel1.BoundsRect, SpinEdit1.Value, True);
end;

end.

As you can see, defining and setting regions is pretty easy. Look in the help file for in-depth discussions. If you belong to the MS Developer''s Network, the library CDs discuss this topic comprehensively.