Your instructor will assign your ID and password to you. The Password is your student ID number, the six digit number you use for registration, etc. Do not forget this or you will not be able to take the exam. There are 30 to 50 questions. If you take one minute per question, it will take the better part of an hour to complete.
Some people can complete it in less time.
You cannot do part of it and come back later. The exam is closed book, closed notes, closed search engines, etc. You are on your honor to take this independently. When you get the page, there will be a login box in the upper left hand part of the page. Blackboard will then welcome you with your own personal page.