OpenSCAD is not what most would consider a conventional CAD package. In most CAD programs to create a shape you have to in some form draw or sculpt the desired shape; this is not the case in OpenSCAD. In OpenSCAD shapes are defined by functions and you don’t draw shapes but program them. Each 3D model is defined by a script that is then compiled into a 3D shape. It is after all called The Programmers Solid 3D CAD Modeler.