This is the easiest way to make a baby sling.
No sewing, just cut and tie.

I made this sling to carry my 9 month old boy on my hip.
I don't recommend this sling for any other ways of carrying, because I'm not sure the fabric will hold; so please be careful.

Step 1: Cut the Shirt

Choose a T-shirt that you or your husband don't need.
Don't pick something too old or torn.
Cut the shirt from armpit to armpit, as shown in the picture.
The sling is the bottom part, the rest goes to recycling.

Step 2: Tie

This step is meant to adjust your sling's length, so that the baby will sit on your hip. The place of the knot depends on the size of the shirt, type of the fabric and your height.
I used simple single knot, and I tied it almost in the middle of my sling, because I'm short.

After you tie the knot, you should stretch the fabric until the knot is really tight!

If you used a funky shirt you may proceed to the next step, but if you used a gray and sad shirt like I did, this is the time for some decoration work!
(I'm too lazy to do it right now, but one day I'm definitely going to draw a bear on it :) )

Step 3: Put Your Baby In!

Put the sling over your shoulder, like a bag.
Put your baby inside the sling and stretch the fabric under his bottom and over his back.
For better support, turn over the fabric above your shoulder and stretch it over the whole shoulder, as seen in the picture.

That's it!
Keep support of your baby's back all the time.

Have fun!