Extrude: Solid, Surface, path extrude - Autocad 3d basic tutorials part 2.

EXTRUDE (Command):
Creates a 3D solid from an object that encloses an area, or a 3D surface
from an object with open ends.

Mode:
Controls whether the extruded object is a solid or a surface.
Surfaces are extruded as either NURBS surfaces or procedural surfaces, depending on the SURFACEMODELINGMODE system variable.
Height of extrusion:
Extrudes selected objects along the positive or negative Z axis. The direction is based on the UCS that was current when the object was created, or (for multiple selections) on the original UCS of the most recently created object.
Direction:
Specifies the length and direction of the extrusion with two specified points. (The direction cannot be parallel to the plane of the sweep curve created by the extrusion.)
Path:
Specifies the extrusion path based on a selected object. The path is moved to the centroid of the profile. Then the profile of the selected object is extruded along the chosen path to create solids or surfaces.
Taper angle
Specifies the taper angler for the extrusion.