With the sling on one shoulder, hold out the inner and outer fabric.  Slide the baby horizontally between you and the fabric, so that the fabric covers the baby's body and goes underneath him where it goes around to your back.

Pull the sling open so that it covers as much of the baby's body as possible.  In some cases, you may need to support the baby's head with one arm.

You can use this position to nurse with either breast, simply by putting the child in the opposite side of the sling.

You can use this position to discreetly breastfeed any size of baby or child.  It's also a great carrying position for a newborn.