How do Voodoo Dolls Work?

From what I’ve read, a voodoo is a representation of a victim, and what happens to the doll, happens to the victim. They’d normally need to be made with some skin, hair, or fingernails from the victim. So, if you poked a voodoo doll in the head, the victim should get a headache. Course, I’ve read A LOT of things, and some things aren’t true.