Hello Vishal ;

There are mane fields you can go into after you complete 12th. In a particular Field there are might be more than 1 exams. But I'd like to keep it as simple as possible.

Engineering :

Purpose - For Admission in B. E./B. Tech., B. Arch., B. Planning
Eligibility - Class 12 pass (PCM)
Application mode - Online

JEE Advanced
Purpose - Admission in UG programmes in IITs and ISM Dhanbad
Eligibility - Class 12 Pass (PCM)
Application mode -Online

BITSAT
Purpose - Admission in Integrated First Degree programmes in BITS Pilani, Goa & Hyderabad campuses.
Eligibility - Class 12 pass (PCM)
Application mode - Online

MBBS :

Application mode - Online

Marine, Nave , Defense :

Indian Maritime University Common Entrance Test
Purpose - Admission in Diploma in Nautical Science (DNS) leading to BSc. (Nautical Science)
Eligibility - Class 12 (PCM)
Application mode - Online

Indian Navy B.Tech Entry Scheme
Purpose - Admission in Indian Navy B.Tech course
Eligibility - Class 12 passed
Application mode - Online

Indian Navy Sailors Recruitment
Purpose - Admission in 24 weeks Basic training at INS Chilka followed by Professional training
Eligibility - Class 12 (Maths and Physics/Chem./Bio/Computer Sc.)
Application mode - Online, By Post

Defence
Indian Army Technical Entry Scheme (TES)
Purpose -Technical Entry to Army
Eligibility- Class 12 PCM
Apply- Online

National Defence Academy and Naval Academy Examination (I)
Purpose - Admission to Army and Air Force wings of NDA and 4 years B. Tech course for the Indian Naval Academy Course (INAC)
Eligibility- Class 12, 12 Passed
Application mode - Online

Depending on the field that you want to pursue there are many exams for you!

Hope this helps!