how to use layers in catia? then how to relate this catia layer into autocad?
In CATIA V5, drawings and parts have Layers that are numbered 0 - 255. They are typically not used, as there are other ways to group and filter things with CATIA. There are no standard assignments of layers, unless your company (or customer) has defined them.
If you want to use layers, drawing and part elements can be assigned to a layer by using the properties panel. You then have to define a Visualization Filter to define if the layer is shown or hidden.
Why do you want to use layers?