Mary gave the green scapular mainly for the purpose of the faith; getting it or increasing it.
The other two purposes are protection from the devil, and a peaceful death.
Mary is the one who stated what the green scapular was for.
However, you may use it for healing or for other intentions as you would any other prayer. But that is not specifically what Mary gave it to us for.
As an example, I gave one to my brother whose wife couldn’t conceive. And this condition lasted for several years. And within a very short time after putting the green scapular under their pillow, his wife conceived. So it can work other ways, but it is mainly for the faith.
Mary did lay down certain requirements. Have it blessed. To say the prayer on the scapular each and every day, “Immaculate Heart of Mary, pray for us now and at the hour of our death.” This is best said by the one who has the scapular, but if not, then the one who gave it to them. The scapular must be with the person, or close to the person, like in their bedroom, or family room, or pocket, wallet, purse, under the mattress, and so on. And one final requirement is great trust in Mary. She herself said that this is very important … trust.
The power of the scapular is not that it is a sacramental, but rather that it has the backing of the mother of God. She is the one, her word, that makes the scapular powerful. It is important to follow Mary’s requirements and not just do it any ole way.
I am elderly, and one of my consolations is the green scapular I carry on me always, and say the prayer multiple times a day, for I trust her word when she promised a peaceful death to those who follow her way and use it.