Read the instructions with the die set. Put the shell holder in the press. Raise the ram to the highest point just before the press cams over. Screw the die down till it touches the shellholder. Tighten the lock ring. That is setting up for full length size per Hornady instructions. Measure before and after. Screw the die further in to bump the shoulder further. Back it out to not bump the shoulder as far.

My advice to gain a better understanding is sacrifice a piece of brass to learn. Set the die up as described to full length size, then back it out two full turns. Ink the shoulder on a case with a sharpie. Run it through the die. A portion of the neck will be sized. The shoulder will be untouched. With your head space comparator measure the shoulder. Screw it in a quarter turn more then re-ink and resize. Measure what you get. The ink will tell you when the shoulder of the case makes contact with the die. Keep repeating till you end up with the measurement you are looking for. The neck on your case will be way over worked and should either be discarded or annealed but at the end of the excercise you should have an understanding of what is happening and how to set up your die.