For the purpose of
baby wearing, a sling is a loop of cloth that is slipped over the head, rests on the shoulder and hangs above the opposite
hip. The center of the sling is wide band of cloth for setting the
baby in. It is exactly like something one would see in
National Geographic magazines, as women work with their babies tied onto their bodies.
It is actually very comfortable, as there are no snaps, buckles or leg holes. You just put on the sling and slip the baby into place, then tighten or loosen the leader strap as needed. It packs very easily, makes a great nursing pillow for the early months, can be used as a blanket when baby falls asleep and also doubles as a sanitary place to lay the baby for a quick diaper change.
Mine is so indispensable that I have two, one for the car, the other for the house. You can put the baby in many different positions, facing you, facing out, lying as if in a hammock, on your hip and on your back. Once you get really good at wearing your baby you can change these positions without even taking the baby out of the sling. You can cook, type, do housework, go to the bathroom, hike, nurse discreetly while walking through the grocery store…whatever you need to do.
It also makes the transition into naptime much smoother. I put on some music, sling up the baby and nurse while I sing and sway around. When baby falls asleep I walk over to the bed, bend over until the baby’s back touches the mattress, and then gently slip out of the sling without disturbing the slumber.
Baby wearing exposes your child to the world from a comforting and safe place. I have worn my children to jazz festivals and carnivals packed with people. They cruised the crowds at adult height, where I felt they were far less likely to get pelted by stray ashes and spilled beer (things that concern me when they are in strollers, you never know what could happen when your kid’s face is level with the average smoker's cigarette).
Baby wearing improves coordination and helps you read the non-verbal language of your baby. Touch and motion improve the physical and mental functioning of your child, preferable to the image of the passive baby, lying about, cooing at the wall.
For more information regarding studies on this and some excellent diagrams on how to use a sling, get yourself a copy of The Baby Book, by Bill Sears, M.D.