You will need the following items iron, a pair of small very sharp scissors, pins, and a cutting surface. The first step would be to place your fabric with the wrong sides facing each other you are sewing your first seam on the outside of the garment. Sew your seams together as usual. Then take your scissors and cut away the seam allowance, leaving about ⅛” of the material left. Next, fold your fabric together at the seam so that what you just sewed is sandwiched between the two layers of fabric. (your right sides should be together now). Press with the iron along that seam line. Pin if needed to keep the seam nice and straight. Next, sew along that seam line again, using your normal seam allowance. When you are done, press along the seam with the iron. This is a difficult process, therefore I recommend practicing before you cut your actual fabric.