start this carry (and all others as well) by making a pocket with your sling. pull the inner rail (edge) tight to form a wall of fabric against your body... but not too tight b/c for this carry you will be putting your baby's feet between the sling and your body. you tighten it more once your baby is in the sling.
lift you baby up on your shoulder opposite the rings in a high burp position. then, put your hand up between the sling and your body and grab you baby's feet to pull them through.
continue supporting your child's weight as you spread the fabric under their bottom and up their back.
then lean forward a little as you settle him into a sitting position in the sling. be sure to have your child's bottom below his knees... this insures he is sitting in the sling and will not slip out. tighten if you need to, to be sure their weight is above your belly button... this will be more comfortable as it distributes the weight. note how the rings have moved down my shoulder toward my baby. to adjust the rings back up to a corsage position simply lift your baby's weight from inside the sling fabric as you slide the sling around to get the rings away from you baby with you other hand.
be sure to tighten the sling so that your baby is snug against you. pull excess fabric around toward the rings and lift the top rail (edge) of fabric on the tail up and out and then down to lock the fabric in the rings.
there you are! sure beats holding that baby up with just your arm and hip!
to get the baby out of the sling -- lift up their weight with one hand as you separate the rings to loosen the fabric. it is a good idea to only loosen it enough to pull your baby up and out... that way it will be close to the right tightness for next time you put your baby in the same way.