The knots or beads enable the witch to do repetative chants without having to keep count.
The Ladder helps the witch to focus will and energy on the desired goal.
Sometimes feathers, bones, and other trinkets are braided into the string as symbols for a desired spell effect. An earlier version of a witch's ladder consisted of a rope or cord of three, nine, or thirteen knots.
The witch's ladder can be created a section at a time or all at once. Either way, special chants are spoken during the creation process to empower the talisman to do its creator's bidding.
A Witches' Bible: The Complete Witches Handbook
WITCHCRAFT
PARALUMUN