Hey I need help with this problem

Let R be an equivalence relation on S. For any 2 members x and y of S, define x http://w2.syronex.com/jmr/tex/img/simeq.latex.gif y provided that x and y belong to the same member of S/R. Then x http://w2.syronex.com/jmr/tex/img/simeq.latex.gif y if and only if xRy

I am hoping some one can guide me step by step to figure out this proof since I do not know how to even start this thanks.