This is super easy, but it takes a LOT of fabric. So before you make one, figure out how much it will cost to buy the fabric (mine was $12.99/yd before my 60% off coupon at Joann's. So in the end it was $26 for two wraps). If you can't get some for a good price, it might be worth it to just buy one (I've seen them at target for a little less than $50).
Here is what you need:
5-6 yards of stretchy knit fabric
Sewing machine and thread (optional)
1 sleeping baby (recommended)
Basically all you do is lay out your fabric, and cut it down the middle *hot dog style, and wah-lah, you have two wraps! You can leave it like this, because knit doesn't fray, it just rolls up a little on the edges.
But...I decided to go one step further and make this a bit harder on myself (only because I got this cool new double needle and wanted to try it out). It is great for knits. The front looks like two straight lines, but the back is all zig zaggy, so it can stretch with your fabric. Fold over the edges 1/2" and pin into place. I usually just eyeball these sorts of things. Sew away, around all 4 sides (5 yards takes a long time to sew), and you are done.
Here is the tutorial I used to learn how to wrap it.
*hot dog style means length-wise, the long way. Did your elementary school teacher teach you this? Hot dog style and hamburger style?