Use this technique for seaming two edges together, such as when joining a shoulder seam. Hold the edgestitches on two separate needles with right sides together.
With a third needle, knit together a stitch from the front needle with one from the back.
Repeat, knitting a stitch from the front needle with one from the back needle once more. Slip the first stitch over the second. Repeat knitting, a front and back pair of stitches together, then bind one off.