Your English is quite choppy and a few words don't make sense in the way you have used them .... but I'll try my best here.
Shoulder movement, or any kind of movement you ask from your horse, should come mostly from your seat/weight and legs. You should be able to move your horses shoulders, hindquarters, and ribcage independently of each other.
So if you wanted to move the shoulders to the left: Keep your right leg OFF your horse to "open the door". You may need to use some supporting rein in the beginning to keep your horse form moving forward, and to help them understand that you want the shoulders to go to the left. With your RIGHT leg, move it slightly forward from your normal "middle" position and bump your horse with your leg or foot. Keep a steady bump going (do not kick harder) until you horse makes one teeny step in the correct direction (left). Timing is critical. You must stop bumping your horse the very instant you get a correct response. Or else the horse will not learn what the correct response is. When you horse is consistent at moving one teeny step when you ask, start asking for one normal step. When she is consistent with one normal step, then start asking for two normal steps, with the proper cross over.
You use this same technique to move the shoulders the opposite way, or to move the hindquarters, or to move the ribcage.
Ideally, you should be able to move every part of your horse's body (shoulders, ribcage, and hindquarters) before you even start on the barrels. In this case, you're already running barrels so it is osmething you can do to better the horse's training.
Moving the shoulders really has nothing to do with the head and neck. If you are doing a proper rollback, and head and neck stay pretty straight. However, if you are running the barrel pattern, and you want to prevent your horse from shouldering into the barrel, you need to tip the nose to the inside, and use your inside leg to move the horse's ribcage (and shoulder) away from the barrel, which keeps the proper bend in your horse's body for the turn.
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.