Tools such as the Burndown or Burnup Chart or Cumulative Flow Diagram (CFD) can help the team (***THIS IS A KEY AGILE MINDSET CONCEPT CENTERED AROUND THE TEAM AND INFORMATION RADIATORS***) determine their progress or how much value they've added.
Velocity is a historical measurement of how much a team can take up during an iteration, the team's capacity for work. It is derived historically, over 3 or 4 iterations. It's intended to be a simple planning tool that's used during iteration planning.
For the purposes of the exam, know all of these tools well as the exam will likely ask situational questions for each of them. When I took the exam, there were 4+ questions where either a Burnup chart, a Burndown chart, or a CFD diagram was presented along with a scenario asking what would the Scrum Master do the given situation or what would be the best course of action to take. If you've purchased the Prepcast Exam Simulator, it will definitely help you prepare for the exam as it contains many questions such as these.