Hi, Susie,
You've probably already heard that kitties learn to knead when they're nursing...but a lot of cats will continue to knead all their lives. Mine is nearly 13 years old and does this all the time! She especially likes to knead a blanket that's become her pet bed- I think it has to do with the feel and/or smell of the material. I've heard of cats that will suck or chew wool, but she doesn't seem to care for it.