OK here it is:
Questions are grouped into sections...each section is grouped into buckets of difficulty. As you answer questions correctly in a section the next question comes slightly harder, as you miss the next one is slightly easier. Depending on what bucket you are in at the end of the section determines your score for that section. You must answer all questions, blank questions are wrong and deduct your score at the end. You can not see the next question without answering the question at hand.
Haphazard guessing is a bad idea, at least make educated guesses.