Hello Ayush,

JEE Mains is an annual exam that is conducted by the National Testing Agency and the CBSE for admissions to undergraduate engineering courses in NITs, IIITs, GFTIs and other institutes. It also serves as the first stage for admission to IITs through JEE Advanced.

The JEE Mains exam has no relation to the SSB interview. In order to be eligible for the interview, you must first of all have qualified the written NDA exam.