Hey,  you need not to wporry if you are a beginner.  You can get every information about NDA and even you can download the free ebooks as well from the following link : 

https://competition.careers360.com/exams/nda?ici=about-exam-t_linking

Well , coming to the point,  the best suggested books for NDA preparation are : 

Pathfinder for NDA & NA Entrance Examination National Defence Academy/Naval Academy Conducted by UPSC (Paperback), 
Study Package MATHEMATICS NDA & NA (National Defence Academy & Naval Academy) 
Entrance Exam (Paperback), NDA (Hindi) (CD-ROM).

Hope it helps!