After completing a MBBS, you will need to pass 3 (very difficult) USMLE medical exams, step by step. Then you apply for residency, which lasts 3-6 years depending on your specialty. And then you can start looking for a job! Please note, that a job does not mean you can stay in the U.S. indefinitely; you will be on a temporary worker visa.
More details here http://www.ecfmg.org/
By the way, all this information is easily found through Google.