This functionality allows to generate 2D mesh elements as a skin on the existing 3D mesh elements.
To generate 2D mesh:
From the Modification menu choose "Create 2D mesh from 3D" item, or choose from the popup menu.
The algorithm detects boundary volume faces without connections to other volumes and creates 2D mesh elements on face nodes. If the mesh already contains 2D elements on the detected nodes, new elements are not created. The the resulting dialog shows mesh information statistics about the newly created 2D mesh elements.