Hello !! 

Nda and Na are the two exams which are conducted twice a year by UPSC to recruit male candidates in INDIAN NAVY , INDIAN AIR FORCE AND INDIAN ARMY wings of NDA . You need to have a good command over general knowledge as the questions of this exam check the candidates on currents affairs , general knowledge regarding physics , chemistry , social studies ' geography etc. Only boys are eligible for NDA AND NA exam since national defense academy doesn't recruit girls in it.

Hope it helps!! 

All the best!!