Both the seam stitching and the seam finish can be sewn independently of each other or sewn at the same time.
The seam stitching appears like normal stitching on one side and as a chain stitch on the other side of the fabric.
Five Thread Seam
This is a five thread seam sewn on a serger.
Five Thread Seam
Debbie Colgrove, Licensed to About.com