NDA

To join NDA, you have to take the National Defence Academy exam conducted by UPSC every year twice, once in the month of April and another in the month of September. The syllabus for the National Defence Academy exam is based on class 11th and 12th mathematics and your general ability test. For general ability, you should have basic knowledge of science, history, politics, economics, geography and basic current affairs. After the written test, there is an SSB interview which took place for 5 days after SSB interview is a candidate passes it then he goes for a medical exam after clearing the medical exam they have to wait for the merit. If the name comes in the merit, Call Up Letter is received and they have to join the NDA.
I hope you crack the exam.

Unfortunately, girls are not eligible to join NDA, in-spite of we woman getting in every stream and proving our-self, this discrimination is bad, but unfortunately we have to abide it. You cannot be appearing for NDA as girls are not allowed to get into defence after class 12th. However, the good part is that one can continue their dream to be a part of defense after graduation through various entries, which are as follows:
You can join OTA as an officer through CDSE entry. You can join IAF flying branch through SSC and AFCAT. You can be a ground officer in IAF through CET. If you do your graduation in engineering then you can have opportunity to move to technical field through EKT.

Hi Ravi!
Except for NDA exam, You can get into Indian Defence Academy through following ways:
Through 10+2 B.Tech Entry: This is a new entry of Navy. SSB calls are made directly to male candidates having the 12th percentage above the cutoff percentage. Selected Candidates will be inducted as Cadets for four year B Tech course in Electronics & Communication or Mechanical Engineering at the Indian Naval Academy, Ezhimala Kerala. During the course, Cadets will be allotted Executive or Engineering including Naval Architect specialisation or Electrical Branch. On completion of the course, B Tech Degree will be awarded by Jawaharlal Nehru University (JNU). Through CDSE: Male graduates who have B.Sc. With Physics & Mathematics or Bachelor of Engineering can apply for Naval Academy (See CDSE Eligibility for details). The written exam consists of objective type paper having Maths, English and GK. The successful candidates of written exam are called for SSB and further for medicals. Other Graduate Entries: Through this graduates and final year students (Pre-final year sometimes for UES as well) can apply. There is no written test, the calls are directly made for SSB based on the cut-off percentage of the qualifying exam. There are many entries for all types of graduates in Indian Navy. However, you have to keep a watch on the advertisement of the applications in the newspapers.