If you will be in the U.S. for a maximum of 3 months you must have a valid driver's license from your own country, additionally some states require an International Driving Permit (IDP) from foreign nationals. That having been said, driving in the U.S. with just your foreign issued driver's license can be problematic since the authorities might be unable to read it if it is written in a language other than English, so getting an IDP is recommended. If you will be staying in the U.S. for more than 3 months, then once you attain residency in the state in which you are living, you must apply for a driver's license there.