The general extrusion block form is probably the most useful form. You create a general extrusion block by drawing a perimeter using a number of pre-defined shapes and then extruding the perimeter by whatever distance is required. If you use the polygon perimeter shape you can create extrusions in both horizontal and vertical planes (or even in sloped planes).
The various methods of drawing general extrusions are explained under Adding Blocks. Circular and rectangular perimeter shapes are used to create cylindrical and rectilinear prismatic extrusions from horizontal planes:
