Here is a brief explanation of the Control Sets.

The Element Switch selects which elements are effected by the Control Set.

However some destinations ( like Main Volume, Reverb, chorus and effects) can not be selected individual for each element. In that case, there is a just a row of lines in Element Switch.

Source is the physical controller that controls the Set. So these are the mod wheel, pitch bend wheel, foot pedals, After touch etc. There is a list on page 134 of the Manual.

The destination is what is controlled. There are 62 different things that you can assign control sets to. They are listed on page 39 of the Data List.

The Depth is how much the destination is effected by moving the physical controller.

One cool thing is that you can use the 6 control sets to assign 6 different destination to 1 physical controller. That way when you move the Mod Wheel for example, 6 different parameters are all changing at once.