[2 Edges] command generates a surface with 2 curves specified, which make 2 edges of the surface. The relative positioning of the 2 curves defines how the edges make the perimeters of the surface.
When the two curves do not intersect at their end, the surface will be Ruled Surface
When the two are connected at their end, one of the two is translated parallely to the other one's end. Thus four edges are obtained and the surface is made just like the surface of 4edges.
For the prompt
"Specify Curves"
, select two curves one by one, that make 2 perimeters
of the surface.
When the second curve's selection is done, the command generates a surface to append it onto the document.