The USMLE (United States Medical Licensing Examination) is the exam series used for medical licensure in the US. It has three Steps: Step 1, Step 2 CK (Clinical Knowledge) and Step 3. It is sponsored by the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners.
For IMGs, passing Step 1 and Step 2 CK is part of the requirements for ECFMG Certification. Step 3 is usually taken later and is required for licensure in most states. Step 1 is reported pass/fail only.
Registration and policies change, including who handles IMG registration, so use the official USMLE and ECFMG pages for current details. See the Step 1 guide and USMLE eligibility for IMGs.