This is a very short video showing how to knit a stitch through the back loop. This creates a twisted stitch. This technique is sometimes used when you need to tighten the stitches of the previous row – for example when knitting stitches that we picked up in the previous row or round (e.g. on the sides of the heel in a sock).
Sometimes, new knitters knit all stitches through the back loop by mistake.