sorry, i'm not very clear about your meanings.
what should i do first?

yes, just like a scientific model of Skin.
I'm trying many times by using Polygon Modeling, but I haven't successed yet.
Need I creat each layer separately? and then lap them togother?
thanks

I'm a newbie. I've project to creat a simple skin model with 3-layers sturcture. Someone can tell me what skill should be used to achive this aim? Polygonal Modeling, NURBS Modeling or others? please...

I'm a newcomer begining learning Maya, thanks for your references.