To clear up - OSCE is not a book. It's an acronym for "Objective structured clinical examination."
It's a way to test a student's clinical skills in a structured setting - most medical schools incorporate it in one or more exams during the clinical years ( at my school we did it for ObGyn, Internal med and Surgery). If You've been tested with OSCE, then step 2 CS may seem a bit easier...
The only book you need for step 2 CS is FA for step 2 CS. Read it, and do the practice cases - preferably with a partner (at least that what others say - I did it on my own, and I'm not a native English speaker, and went to medical school in Europe, and I passed).
Good luck with the test.