Well Ill try to be as short as I can - I have an exam in descrete maths, but sadly our discrete maths course isnt compatible with general courses because it has other stuff included in the course aswell. I have prepaired the entire exam 3 times for now, but every time I had just 1 part left that I couldnt finish, which is recurent relations and generating functions. I complete all the other parts and get so overwhelmed when I get to this one that I cant even describe it. The problem is that there is so much stuff I know nothing about, that I dont even know where to start. I passed my calculus exam without deep study, just did it to pass the exam and that left me crippeled for many courses to come. I do have planned to revisit the Calculus parts from scratch, but now its simply not the time because the deadlines are coming closer. I need to know, in detail, which are the prerequisites that I must learn before being able to tackle generating functions, because just knowing what I have to do would make the whole thing so much easier. Study resources are welcome aswell, but I dont want to be greedy here. Tnx in advance!
The main prerequisite for ordinary generating functions would be a concrete understanding of sequences, Sigma notation / manipulation and the various closed form expressions for common sums, basic differential calculus including Taylor Series and knowing what a power series is.
Assuming you have a decent Maths background you shouldn't have too much trouble in covering / refreshing these topics in a day or so.
I would also add that while not a prerequisite, an understanding of Recurrences (Divide & Conquer and Linear) may help you understand why Generating Functions are used.
MIT have a great 25 page document on Ordinary Generating Functions that you may find helpful. It is part of their wider Discrete Mathematics course. Link here