Pendulums have been used in divination since time immemorial. A pendulum can only give yes or no answers, so you can only ask questions which are based in clear cut dichotomy. The pendulum is very bad at nuance and it is unwise to make life choices based on its response.
Hold the pendulum steady and wait until it stops swinging. To get to know your pendulum ask some yes or no questions that you salready now the answer to -- for some "yes" may be a circle, while "no" moves back and forth. When you feel that you are receiving constistent responses to known questions, then move on to the unknown.