Set ShapeTool property as SpEllipse,then you can draw it by mouse.

Also,you can draw it by code.

Code example:

procedure TMainFrm.Button1Click(Sender: TObject); 
begin 
  if MyCAD1.GetShapeByName('EllipseShape') = nil then 
    MyCAD1.AddShapeByCode(MyCAD1,spEllipse,'EllipseShape',[MyPoint(380, 261), MyPoint(430,261) ,MyPoint(430, 320),MyPoint(380,320)]); 
end;