Hey,

After passing your 12th grade you can appear for NDA exam conducted by UPSC. Though you can only apply for The Army wing of NDA if you don't have maths and physics in your 12th as your subjects. Another way to join Indian army is after your graduation through CDS. The education qualification required to join the Indian Army and fill the application form of CDS is graduation while the age limit for CDS is 20 - 24 years. Both male and female candidates can apply for CDS. Candidates applying for the Air Force need to have Physics and Mathematics at 10+2 level and those who are applying for Indian Naval Academy must have an engineering degree.

You can also go through the link below to get a detailed analysis of the same-

https://competition.careers360.com/articles/How-to-join-the-Indian-Army

Hope this helps.