Multiple steps required, each more daunting:

1. Study well in +2. Crack the NEET/AIIMS UG Entrance and get a good college.
2. Pass all your exams in 4.5y of MBBS, preferably doing well in order to create a good CV.
3. Complete 1y compulsory internship, all the while studying for NEET/AIIMS/PGI Entrance.
4. Crack the PG entrance and take internal medicine (3y PG)
5. Pass the MD final exam.
6. Crack the DM Entrance (MCQs+ interview).
7. 3y DM Neurology and pass the final exam.
8. Voila! You will become a neurologist.

It is a difficult path and requires great focus. I'm at step 3 and have the same aim.

All the best for your future.

PS If you are interested in neurosurgery, AIIMS offers 6y MCh program directly after cracking PG entrance that will prevent many exams.

I also hope you are clear on, how few seats AIIMS and other reputed institutions offer for such courses and hence the competition is immense.