An incident edge is an edge that starts at the current vertex. The reason that you need to act on these is that the server does not automatically create edge info for a vertex; you need to pull the edge information out of the cogroup (out of the edgeTableIterator) and call vertexState.addEdge() with an Edge object that you have created based on that info from the edgeTableIterator.
You can get multiple values (rows) out of the vertex iterator.