As you are an intermediate student, then your age must be under 19.5 years, so you can appear for NDA writtene exams. After clearing the written one, you'll be called for SSB Interview. Upon clearing SSB Interview and medical Examinations, you can see yourself in Army. Another way to join army is to appear for CDS. For CDS, candidates must have to complete their graduation first. A bacehlor's degree from a recognized University is required in order to be eligible for CDS. Another option is Technical Entry scheme. Candidates who have passed 12th with minimum 70% marks in aggregate in Physics, Chemistry and Mathematics are eligible to apply for commission under the 10+2 Technical Entry scheme. Another option is Entry for Technical Gradutes or post graduates. After clearing SSB and medical examinations, candidates have to undergo a long training at OTA. Candidates who are able to complete the training, are posted under Short Service Commissioned officers. http://competition.careers360.com/articles/cds-eligibility-criteria
http://competition.careers360.com/articles/nda