Extruding can be done on lines, curves, or faces. An extrusion is specified by a vector:
extrude <x> <y> <z> extrude <faceNum> <x> <y> <z>First draw a curve while in insert mode (hit the i key). Complete the curve by hitting right click, or enter.
Then extrude the line.
extrude <x> <y> <z>
Now turn on face numbers to determine which face to extrude.
view fnums
Pick a face and specify the vector.
extrude <faceNum> <x> <y> <z>