Hemming stitches are used where two pieces of knitting are joined one behind the other, either where two pieces of a garment overlap at the front or if a hem is folded up behind the base of a garment. Sometimes to avoid hemming the two pieces of work are knitted together, but this can be vert tricky in miniature, so hems are used.
The needle is inserted under the back loop of a stitch on the front piece of knitting and then taken back into the back piece of knitting:
The stitches are not pulled tight and NEVER go right through the front piece of knitting:
The front of the garment will appear like this, with no stitches showing on the front of the garment: