If your Exams tab screen looks like the below screenshot, it means that you have not attempted the exam yet.
Under Attempts, it says 1/3, which means that you are on your first of three attempts.
Under Status, it says "Not Started," which means that you have not yet started this attempt.
Once you click the "Start Exam" button, the exam timer starts and cannot be stopped. Please do not click this button until you are ready to finish the entire exam.