If you are not strong on the fundamentals of what you are going to learn or study, you won’t be able to understand it properly. Imagine learning advanced problems in trigonometry without properly knowing the basic ratios of sine and cosine and the basic relations. Or imagine learning rules of grammar without properly knowing the parts of speech.
The fundamentals could be the ones taught during the beginning of the chapter, the beginning of the course, or even during the earlier years or semesters. You need to identify where you stand and revise the fundamentals accordingly. Don’t hesitate to revise or relearn or learn even alphabets if needed. Put in extra effort and take extra coaching in case it’s necessary.
Remember, without a strong foundation (i.e., fundamentals), your building (i.e., present studies) cannot stand the earthquake (i.e., exam).