If you're trying to differentiate the MBE (Multistate Bar Exam) and the UBE (Uniform Bar Exam), the MBE is a portion of the UBE, which also includes the Multistate Performance Test, and Multistate Essay Exam. I think almost every (if not, every) state in the U.S. requires the MBE as part of their exam requirements. If you sit in a UBE jurisdiction (only a handful sprinkled throughout the country), you would take all three portions. The benefit to taking the UBE is your score is more portable, meaning you could take your score and qualify for admission to any other UBE-accepting jurisdiction (assuming you meet the local requirements: character and fitness, MPRE score, etc.)
You can find more information at the NCBE website. Good luck to you.