CBT is basicly off road training first, by that i mean in a school playground or something similar to that size wise, where they will teach you how to handle moped/bike, moving off, breaking, emergency braking, turning and so on. This usually last a few hours depending on how many people are doing the cbt and how well everyone progresses.
After the initial training above you then go onto the roads, where the instructor will see how well you handle the open roads, they will ofcourse talk you through this before heading out, you will have an instructor in your ear telling which route to go (its only 1 way comms though).
Thats it basicly, generally takes half a day, one thing I would say is don't be scared to ask any questions to the instructor/s. They are there to help you through it.