I think you might be talking about "french seams". You put the fabric - Wrong sides together, sew 1/8" seam. Then turn so fabric is right sides together and sew a generous 1/8" seam. This finishes the seams so no raw edges are shown. This is how my mother taught me, but when I do it, I actually like to take a little bigger seam than the 1/8" so I allow for using a 1/4" seam each way when I cut the fabric.