A "voodoo doll" is another term for a "poppet." Often, "voodoo dolls" is seen as improper because of the many stereotypes of Voodoo, the New Orleans religion. Poppets are a European type of charm which represents an individual. It's sympathetic magic, whatever is done to the doll is being sent to that individual. The how and why it works is based upon personal belief.
Poppets are not an all powerful device used to control a person's individual body parts or to instantly hurt people by sticking needles into the doll. It's just a representation of an individual. They can be made from corn husks, sticks and moss, paper, clothe and herbs, cookie dough, or pretty much anything. People can get really creative with poppets.
What is known in movies as a voodoo doll is something called a poppet, which is used in sympathetic magic. They do not work like in the movies. A pin to the chest of the doll will not cause harm to the person it represents. It is a means of focus and direction of energy, so to speak. Everything related to it is basically symbolic.