Certain classes have proctored exams. To see which ones need this exam you can check through your portal. In each class section you see what exams/discussions/projects you need, at the very bottom you will see the exam: Proctor Exam.
For ex (taken from my Precalculus class):
 Mat 222 Proctored Exam |  |
You will not be able to take this exam online since you need a proctor to be with you. The only way you will be allowed to take it online is if the exam has the option for Remote Proctor.
I hope I didn't confuse you and was able to help you.