If you fail a quiz, don't stress; quiz scores do not limit your ability to complete the course. Quizzes are intended to help you review the lesson content before the exam. They do not count toward your final score for the Course.
If you fail an exam, review the course lessons and quizzes and you can also consult with your training manager to get clarification on any issues you may have. You can usually take Course exams twice, but this sometimes depends on the Product and could be limited to once. If you see a "retake the exam now" link, then you can click that and take the exam again when you're prepared to do so. If you are a Staff user and have failed the exam twice and are prevented from taking the exam again, you will need to contact a Manager or Administrator on your Account to reset your exam for you. Staff users will find a list of those Managers and/or Administrators available to do this on their Profile page.