Workflow in .net layered architecture

Question

Hi friends,
             Am new to workflow technology,I want to implement the workflow in my product development.

1.How to use the workflow in layered architechture?
         
       Note:My layers are Presentation,Service,Business,Data.

2.Which layer is best to use workflow and how to use it?
 
please explain from basic level.

                                                             Thanks in advance