first stage.PIB TA
1. you need to study NDA, CDS old solved papers on all subjects. Math and bioloby is not compalsory.(with out math and biology study all old papers)
2.for intervew you have to explane your present job what are you doing today and they ask you questions only on your present job knolodge.
2nd Stage SSB
There are many books and coaching centers in the india.