After graduating from medical school outside the US, you will first need to take the USMLE, then you will need to complete a medical residency in the US in your field of specialization. After that, you can be licensed to practice medicine in the US.
Within the US, each state’s medical board determines which foreign medical degrees are acceptable for physicians who want to practice in that state. Here are some links:
http://www2.ed.gov/about/bdscomm/list/ncfmea.html#top
http://www.mbc.ca.gov/Applicants/Medical_Schools/Schools_Recognized.aspx
https://medicalboard.iowa.gov/licensure/permanent.html