Mathematics is essential for chemistry for several reasons including carrying out proper experiments in the laboratory & obtaining useful products in industry.
Calculations for chemical purposes may be very simple or they may be more complex. I would not say that the professor is terrible but I think this person may lack the correct approach of passing on the information to the students. This is a widespread common phenomenon because many professors lack a background in the art of teaching "that is made by an educational degree or a degree in professional teaching".
To overcome this problem, my advice is to do two things: 1) Look at examples in the textbook as well as the internet & try them before you see how they were solved. If your answers are incorrect, re-read the sections & try again until you reach the given solutions. 2) Collective study, with one or two classmates, may help a lot with each one of you exchanging ideas. Sometimes, friends are better than professors in putting across certain ideas in a simpler mode. Best wishes for success.
Depends on the level you want to study, we essentially apply some "mathematical tricks" to solve physical chemistry problems, you can study for the following two textbooks:
YATES, Paul. Chemical calculations: mathematics for chemistry. CRC Press, 2007.
MCQUARRIE, Donald A. Mathematics for physical chemistry: opening doors. University Science Books, 2008.
It may help to stop and think about the big picture. What are you trying to really do? I've often found that my students focus so hard on the small mathematical details that they lose track of what the question they are trying to answer is. In the physical sciences, we quantify, that is use set quantities, to identify relationships between different bits of information.
In classes like physical chemistry, it's all about word problems. The first step to solving any word problem should to be to identify what you are looking for. The second is to identify any information you are given about what you have, is it adiabatic and reversible, are you dealing with a particle in a box in a single dimension, are you trying to identify the order of reaction and you have two half-lifes with their concentration? From there it is a question of what can you use from things you already know to solve the problem.
You are probably past the point where you need the primer, but sometimes we do need a refresher. For thermo, https://www.amazon.com/Conceptual-Guide-Thermodynamics-Bill-Poirier/dp/1118840534 this is a good book to help with the conceptual framework. For kinetics, most textbooks have a fairly good set up. For quantum, if you haven't taken it, then you should go look at three dimensional calculus, possibly vector calculus with a lot of trigonometry to get more comfortable with it. There really isn't a better answer for quantum than getting good at doing math in spherical coordinates.