Are you talking about karmdharay samas. If You really are then :-
Just think of it as comparing sometthing to another
It is more like an adjective
Words like hai jo are commonly used for this.
Mrinmay Mukherjee answered this
see its very simple let me giv u an example....... pitamber = pila wastra/ where pila is the visheshan and vastra is the visheshya. therefore in this type of samas der is a relationship of visheshan and visheshya