One can take short courses and pass the FAA exams. I didn't do that, but instead spent a year studying before taking the writtens, then a year preparing for the practical...after working as a mechanic's assistant (apprentice) for seven years. The FAA and the practical test examiner told me that's not the norm, but I didn't want to show up unprepared. My oral exam lasted about eight hours, plus a long practical test that involved timing magnetos, inspecting an aircraft, researching AD's, riveting, bending metal, balancing a propeller, etc.
I know nothing about the Indian exam, but I'd say for any practical test, one should always show up prepared.