With a serger, you would use the flatlock stitch function and line up your 2 pieces of fabric on top of one another. Afterwards, you would press open the seam and one side it looks like a ladder and on the other side, it looks like a tight zigzag stitch and each piece of the fabric is flat next to one another. Great technique for piecing quilts, I think (remember I'm not a quilter) it looks great. On the sewing machine, I would use my edge joining foot with a zigzag stitch but it's a little trickier. It's much easier using a serger for this technique.
Marty
Brighten each corner where you are ... smile!