The first step in the process is obviously to buy nunchucks. Ideally buy a set with a lighter material that will not cause too much damage if you get hit. That is important as it is very likely that you will take a number of blows while you practice in the start.
Do not try to be Bruce Lee in your first week of training and learn the ropes slowly. There is no need for you to learn advance techniques in the start and you must take your time in the initial simpler ones and master them in order to move forward. Take your time and gradually improve upon your set of skills.
Buy a Book
You can also buy a book that illustrates various techniques that can be used. Since these books are authored by expert martial artists themselves, they can take you through the whole process and how to improve your skills over time. Buy a book that martial artists themselves recommend and follow it, you should do well.
You can watch videos of known nunchuck experts and see how they move and how they do it. This can help you in removing errors that you may otherwise be making and will also help you in improving your abilities with the weapon.
Join a School
You can also join a martial arts school in your area. There is no replacement of learning from someone who knows the craft. A good teacher can help you in a big way by enhancing your skills and can be a great help in getting you trained in the right way.