I have read the information about the world edit information quite a few times. But it's just not getting into my head. :(

I want to have a multi layered farm but the location is underwater right now. I have already had one (of my many) questions answered and I just want to be 100% sure of this before I post the application.

I need a replacement of different types of blocks for 3 layers of dirt and then a block removal of 4 layers.

I am seriously confused about it because it says that the replacement blocks can not be air ... but I need space for my precious head. :p Sorry to be a pain with so many questions! D: