You have 36 stitches when you start. For part one you:
Next Row (RS) K1, k2tog, k5 (neck edge). Turn.
That is working across only 8 of your 36 stitches. You stop there and turn to work back over the same 8 stitches (those will be the stitches you work in part 2)put the other 28 sts on a spare needle.
You will also be working parts 3 and 4. You do part one over the 8 stitches and put the other 28 on the spare needle, turn and do part 2 over the 8 stitches, ending up with only 1 stitch.
Then in part 3 you go back to the 28 stitches that are on the spare needle. Put what will be the center 20 stitches of the neck on a stitch holder and with the 8 shoulder stitches you do part 4 which is like part 2 only reversed and it also ends up with only 1 stitch.