Right-angle Seam, or Corner Turns
As with Curved Seams, you're going to want the needle to be positioned down, in the fabric every time you stop while sewing this technique. So, if your machine offers a needle positioning feature, program it now. Otherwise, just remember to move the needle into the fabric before raising the presser foot.
Lay first piece of fabric right side up
Place second piece on top of the first with right sides facing, matching stitch line to stitch line (where you're going to sew) **Angles will not meet** Also, this took me a trial run to figure out, but you want the top fabric to over lap the selvage edge of the bottom: see picture. I suppose this is what was meant by "matching stitch line to stitch line". But as with so much in my life, I had to screw it up first to figure it out. But now? Totally makes sense! :)
Stitch to the corner. Needle down. Raise presser foot.