The shims go between the rocker pedestal and the pedestal retainer rail. They lift the pedestal and rocker off the seat by a few hundreds of an inch depending on which you use. The rail is already about .060" and you will use either .030" and/or .060" shims to adjust your valvetrain geometry from there.
There are a few things to check, mainly the position of the roller on the valve stem and the lifter preload. You need to shim the rocker so the roller's full range of travel is centered of the tip of the valve stem. From there you check your lifter preload. If you have between .020" and .060" you are good to go. If it falls outside that range you need different pushrods.
