To create this seam, use your tapestry needle to pick up the bars between the stitches on the stockinette edge and the furthermost loop on the garter stitch edge. You will see from the video tutorial that sometimes you have to dig around a little to find the bar between the stitches on the stockinette edge. Keep trying, though; it’s in there!
Work flat, on a table, keeping the two sides even. Snug up the yarn as you go – but not too tightly.
Feel free to contact me if you have questions about this seam or about any of my patterns.