Yarn is a traditional item used in Wiccan arts-and-crafts. Yarn is manufactured from wool, a byproduct of the meat industry. It is a stringy substance, somewhat similar to spaghetti, but be careful; yarn is NOT edible. Besides its many questionable artistic uses, yarn can also be used to strangle small animals such as kittens, or for knitting. (Note: sometimes, the kittens will conveniently strangle themselves with the yarn! This saves you precious time and effort.)
Knitting is a process whereby yarn is carefully tangled up with long, pointy needles in such a way as to magically form all kinds of itchy, uncomfortable items, usually clothing. These include, but are not limited to:
Knitting is often practiced by sweet old ladies, Russians, and people who are extremely dull, boring, and tedious. This is OK, because you can use their knitting needles to stab them in the eyeballs and then take their valuable property.