The Extrude action creates a surface by sweeping a cross-section (or “profile”) curve along a path curve. The curves can be normal 3D curves, surface isoparms or edges, trim edges, or curves-on-surface. The ends of the extruded surface are open; however, you can create caps at each end using Surfaces > Planar.
To extrude a profile curve along a path curve
Maya uses the key curve (the last curve you select) as the path.
To cap the end of an extruded surface
To do this, press on the extruded surface, and choose Isoparm from the marking menu. Then click the end of the extruded surface.