United States Medical Licensing Examination (USMLE) is an exam conducted for fresh medical graduates in order for them to receive their practicing licence. It takes part in 2 steps, step 1 being you assesment, whether you can apply the concepts you learnt in med school to actual medicine practice. It is a one day exam divided into 60 minute blocks conducted over 8 hours of a single test session. The number of questions in a single block may be 40 (max) and the total number of questions can be as much as 280.

For medical students who have graduated outside the USA and Canada, you have to apply through ECFMG on IWA (Interactive Web Applications).

You can get the details on their official Website : https://www.usmle.org/apply/