depends on what role you want in the Indian Army. There are a number of different cores in it. Like if you want to join army as an infantry solider then you should go for the CDSE exam which is held twice a year. The exam is conducted by the UPSC. And if you want to join army as engineer then you call apply through the TGC(technical graduate course) entry in which you'll be called for the SSB on the basis of your graduation Percentage/CGPA. There will be no written exam for this entry. And you'll get commissioned to the rank of lieutenant. The third type is the SSC technical entry. Which is quite similar to the TGC entry. There is no written exam for it. You fill up the form and get a SSB call. And then if selected you'll get trained for 2 years and then you'll get commission. The only difference between TGC and this SSC entry is that in SSC entry you'll get a short service commission which means you'll get a service of 10 years which maybe extended for 4 years(not necessarily).

I hope the answer was helpful. Please feel free to correct if I am wrong at any point.