This way of carrying babies is very common in Mozambique, south eastern Africa. It is relatively comfortable and versatile. Plus, all you need is a rectangular piece of cloth (and a baby, or course).
The baby in this picture is 9 months old. I have been carrying him using this technique since he was 1 month old. As he grew, my back got stronger!
Step 1: Find a rectangular cloth
The material should be sturdy but soft. Cotton works well. What is important is that it is rectangular and also big enough (about as wide as your arm span). The cloth pictured here is a Mozambican "capulana".
Step 2: Put the cloth at your waist
Imagine you are going to wear it as a skirt. Just hold it like the picture and then lean forward with your torso parallel to the ground.
Step 3: Baby goes on the back
Lean forward, grabbing the ends of the cloth. Have someone assist you by holding the baby and then putting the baby on your back, face down.
Step 4: Cover baby's bottom and back
In this leaning position, slide the cloth from your waist upwards towards your and your baby's shoulders.
Have the person assisting you adjust the bottom edge of the cloth so that it fits underneath the baby's bum. The baby's legs (from the knees down) must not be covered.
The top part of the cloth will go up to the baby's shoulders (older babies can leave their shoulders uncovered, younger babies need more support).
Take the right side of the cloth and put it over your right shoulder.
The left side goes under your left armpit.
Step 5: Tie in front
both ends of the cloth meet in the front, between the breasts.
tie it twice and slowly come out of your leaning position.