Most traditional jobs for physicians require a medical license.
Becoming licensed as a physician in the United States requires passing a set of examinations and completing training.
In general, USMLE part 1,2 and 3 are required (information here) as well as at least 1-3 years of residency training.
The medical licensing requirements differ slightly for each state and can be found here.
Most residency positions are obtained through the National Resident Matching Program (information here)
There are a few positions available at other times during the year outside the match when unexpected circumstances open a residency position. See a list of updated unfilled residency slots here.
You can find more information about international medical licensing and programs for international medical doctors here
Find out how international medical school graduates can obtain US clinical experience here