The exams you take throughout the class are worth 2/3 of your final grade, and the proctored exam is worth the other 1/3 of your final grade. For example if your average score for the class exams is 85% and your final is 70%, then you would add 85 + 85 + 70 = 240 / 3 = 80% would be your final grade for the class.
You can also calculate like this:
2/3(class average) + 1/3(proctor) = final score
0.67(0.85) + 0.33(0.70) = 0.57 + 0.27 = 0.80 = 80%
As long as your final grade for the class is 70% or above, you pass the class.
If you fail the proctor and want to take it again for a higher grade, you can but the highest grade you can receive on the retake is 70%. PF will take the higher of the two grades as your score.