You said you understand the current circuit...
What do you think they do? How is a normal light circuit wired? If you don't grasp this you should really consider calling an electrician.
Look at the circuit breaker. There is a drawing on the back. What does it show? What do you think it means?
Here is a link for you. It's about basic house wiring in the UK. Their system is a bit different but the section on lighting is sufficiently similar that you hopefully will grasp the concept.
[länk]