Dear Biswajit, now NEET is the only Emtrance Examination for admission into Medical, Dental and Ayush colleges across India. All State level entrance exams have been scrapped in the favour of NEET. Now NEET is mandatory if you want to study MBBS abroad as well. And for being eligible for NEET, you should be atleast 17byears by December 31st of the year of admission and you should have scored a minimum aggregate of 50% in Physics, Chemistry, Biology/Biotechnology. It is 50% for General Category, 40% for PWD and 45% for SC/ST/OBC. Once you qualify in NEET, there will be merit list released. Every college will release its cut off marks for each category. If your score matches the cut off, you apply to those colleges and counsellingbprocess is conducted. Now every state except for Andhra Pradesh, Telangana and Jammu and Kashmir participate in All India Quota which means 15% of their Medical Seats can be occupied by Non Locals. The rest 85% is for Liocal Students. AP, Telangana and J&K have 100% seats alloted for their local students. After the counselling, you take an admission in the college and you study Medicine for the next 4 and 1/2 years after which there is 1 year mandatory internship. 

Apart from NEET, there are AIIMS and JIPMER but they conduct entrance examinations for admissions to their own colleges. They are autonomous bodies. For AIIMS, it is 60% in Physics, Chemistry, Biology and English. The counselling process and admission process will be the same but there is no concept of State Quota and All India Quota.