Cone relations and equivalence relations in the Myhill - Nerode Theorem.

Question

Fix an alphabet ${\bf S}$ and a language $L \subset S^*$. For any two words $w$, $w'$ $\in S^*$, define a relation $w \sim w'$ if and only if Cone$(w)$ = Cone$(w')$. Then prove that this is an equivalence relation on $s^*$ and rephrase the Myhill - Nerode Theorem in terms of this equivalence relation. I am stuck on the problem. I do not have an idea how to start.