Pendulums are a method of divination, the art of divination features the use of tarot cards, runes, crystal balls, scrying mirrors, pendulums and many other methods
Pendulums are very good for beginners who are looking to get their first steps into divination, they provide a quick and easy "yes or no" answer. The tip to using a Pendulum is you have to understand it's "language" as it were, all pendulums have different languages, you need to connect with yours and figure it out.
Pendulum's can be ranged from wooden to crystal material, for example my Pendulum is a quartz crystal, the pendulum itself can have different correspondences accordingly to the material they are made out of, for example if your pendulum has an amethyst stone, then it would probably increase the accuracy as amethyst stones are associated with the third eye chakra which can be channeled for things contain the properties of an amethyst, just as a quartz type would contain properties of quartz.If your Pendulum is made of the Oak then it would be associated it's properties, be it protection, luck, etc.
To understand your pendulums language first obviously you must hold it by its suspender, then ask it to show you how it will move if the answer is "yes", whatever movement the pendulum makes, it will be the set movement for a positive answer. Now you should ask it to show you the movement for a "no" and then the movement for a negative answer will be shown.
This method of divination can take some getting used to, specially if you do not use your pendulum that often. However, they are interesting little divining tools that give you a quick yes or no answer for a current situation.
Enjoy Working with your pendulum's.