After you cut your fabric to 3 times as long as wide, you can hem it, or not. I suggest you do not, on your first one. Then zig-zag the raw edges after. You fold the left third over and stitch the top edge down. You fold the right third in, and be sure to lift the bottom of the left third, so you do not sew it into the bottom seam. Sew the bottom edge. It will look like this . . . then lift the corner, and unfold to reveal your bag.