Basically, the cloud layers are there to end up with a black and white land mass that is used to create masks or selections. If you already have that layer (your background) then there is no reason to go through the steps that are used to get you there. All you need to do is carry on from the point that starts to use that layer. If later steps require use of those cloud layers, I would suggest that you create them at that time. It might also be a good idea that once you have tried the tut with your own B/W layer, to try the cloud method just to see how it works. Knowing that method might help you in the future. You neeeeeeever know....