GroIMP defines the 3D primitive objects sphere, box, cylinder, cone, frustum, parallelogram, plane, and text label. They can be moved and rotated interactively as explained in The 3D User Interface.
NURBS (Non-Uniform Rational B-Splines) are a popular and versatile representation of curves and surfaces. GroIMP contains full NURBS support, e.g., techniques to construct NURBS surfaces out of a set of NURBS curves, including surface skinning, surfaces of revolution, extrusion and sweep surfaces. A detailed description of these techniques will follow in later versions of this manual. For the time being, you can experiment with the surface settings in the Attribute Editor. Of course, you have to create a surface via Objects/NURBS/Surface at first.
The global 3D objects light and sky are contained in GroIMP. They can be placed into the scene similarly to primitive objects. In the wireframe representation, the sky object is displayed as a sphere; its position is irrelevant because it represents a sky sphere at infinity. Visual effects cannot be seen in the wireframe representation, use POV-Ray to get a ray-traced image which makes use of these objects.