At the edge where you wish to begin your narrow hem, turn under the hem allowance. For example, mine is a 5 cm hemmer, so, I turn 2.5 cm twice. Then pin it parallel to the folded edge. With your presser foot up, manually lower the needle into the beginning of the hem and remove the pin. Gently twist the area to be hemmed into the curved part of your foot so that it feeds into the needle in a roll. Then lower the foot and begin stitching. As you feed into the foot, keep the "roll" going toward the needle through the curved part of the foot.