Extrude Along Path – This command allows you to take a cross section object and pull along a planar or NURBS curve. This makes them ideal for creating objects like handrails and picture frames. You can even use it to generate 3D retaining walls that fit to a site model.
The concept of the extrude along the path is that you need to create your path object, and it pays to create this first, and then create the cross section that you want to be extruded along the path. This command does not allow you to change from one shape along the path to another.