element based surface

Dear All

Some one told me to define node-based-surface or element-based surface during defining General Contact in large deformation simulation. I tried my best to figure out how to do it. But i cudn't. I just know  it can be done by editing the .inp file by making an element set. and making a surface from that element set.

Is there there anybody who have done it before?? It will be great help if you can explain me how to do it.

thanks in advance.