hi,

see ssb interview is the last stage to join NDA, SSB Screens the candidates for the Army, Navy and Air Force. The interview involves questions  of psychological tests of personality, to check the candidate's suitability for getting introduced into the armed forces. however you must have good communication skills and show confidence while answering. you may follow the below mention books which would help you to crack ssb interview:

SSB Interview: The Complete Guide

Book by Dr. N.K. Natarajan