Solid, surface, and mesh objects offer different functionality, that, when used together, offer a powerful suite of 3D modeling tools. For example, you can convert a primitive solid to a mesh to take advantage of mesh creasing and smoothing. You can then convert the model to a surface to take advantage of associativity and NURBS modeling.
Start with primitive solids such as cones, boxes, cylinders, and pyramids and modify and recombine them to create new shapes. Or draw a custom extrusion and use various sweeping operations to create solids from 2D curves and lines.
A surface model is a thin shell that does not have mass or volume. AutoCAD offers two types of surfaces: procedural and NURBS. Use prodecural surfaces to take advantage of associative modling, and use NURBS surfaces to take advantage of sculpting with control vertices.
A typical modeling workflow is to create a basic model using mesh, solids, and procedural surfaces, and then convert them to NURBS surfaces. This allows you to utilize not only the unique tools and primitive shapes offered by solids and meshes, but also the shaping capabilities provided by surfaces - associative modeling and NURBS modeling.
You create surface models using some of the same tools that you use for solid models: sweeping, lofting, extruding, and revolving. You can also create surfaces by blending, patching, offsetting, filleting, and extending other surfaces.
Unlike solid models, mesh has no mass properties. However, as with 3D solids, you can create primitive mesh forms such as boxes, cones, and pyramids, starting in AutoCAD 2010. You can then modify mesh models in ways that are not available for 3D solids or surfaces. For example you can apply creases, splits, and increasing levels of smoothness. You can drag mesh subobjects (faces, edges, and vertices) to deform the object. To achieve more granular results, you can refine the mesh in specific areas before modifying it.