Hey Hari,
If you want to join army or navy, you can give UPSC examination for defence called Combined Defence Service Examination. For this your age should be between 19 to 24 years and you must have completed your graduation from UGC recognised university.
You will have following options in CDSE:

• IMA (Indian military academy)
• OTA (officer's training Academy)
• INA (Indian Navy academy)
• AIA (Air force academy)

Since you have done engineering, you can also go for Technical graduate course for permanent commission or you can choose short commission course too.
For permanent commission, training is given at IMA and for short commission, training is done at OTA, Chennai.
For CDS 2020, the application has been closed for the examination which is in February 2020, so you can apply for the CSD 2020 which is going to be conducted in November 2020. Application process will start from August 2020. So, stay updated


Hope this helps!