A pendulum can either be home made by a length of cord weighted at the end with coin or gem (see correspondences for gems related to divination…a moonstone may work the best), or it can be purchased at an occult shop. It would be best to wear the pendulum on your person as if it were a piece of jewellery, that way it will be able to ‘tune’ into you. Also make sure that it has been cleansed and consecrated according to you spiritual path.
In order to begin (we’ll use looking for a lost item as an example here), take the pendulum to the room/place where you think you’ve lost your item. Ground and centre. Ask the Divine Power to guide you to your lost item. Raise the pendulum to eye level, holding it in your power hand (usually the hand that you write with) and ask it a very basic question, like “Did I lose my ring in this room?” The pendulum will begin to swing to give a yes or no answer. When you get the answer, narrow down the questions, like “Is it behind the filing cabinet?” Let the pendulum guide you to where your item is.
Another neat thing you can do with it is, say for example the thing that you lost was in an area too large for you to actually cover in person. Draw a map of the area while strongly visualising it as best you can in your mind. Once finished, hold the pendulum over the map and ask questions like “Is my ring by the road?” Again, the pendulum will begin to swing to give the answer.
You can also ask it questions like “Does Tommy like Suzy?” and things like that. The possibilities are endless. You have to experiment with your pendulum, every one of them is different, as is the person using it.