Following are the steps to become a MBBS doctor:

1 Meet the eligibility criteria. A student must have passed 10+2 Science stream (with Physics, Chemistry and Biology subjects) to be considered eligible to pursue MBBS course. ...

In order to become a doctor you have to appear for NEET exam in order to take admission in MBBS course.

You can also check the eligibility criteria of NEET from the given belwo link

http://www.medicine.careers360.com/articles/neet-eligibility-criteria

You are targeting which year for entrance exam?