Equivalence classes will be the sets of elements of A which have the same value for function f.
eg: if A={1,2,3,4,5,6,7,8} and f={(1,a),(2,b),(3,a),(4,d),(5,a),(6,b),(7,c),(8,d)}
then R={(1,1),(2,2),(3,3),(4,4),(5,5),(6,6),(7,7),(8,8)(1,5),(5,1),(1,3),(3,1),(3,5),(5,3),(2,6),(6,2),(4,8),(8,4)}
then the equivalence classes are:{1,3,5},{2,6},{7},{4,8}