(OCR AS Level) Fetch, Decode, Execute - how is it so difficult to understand it?

New Year 12 here,

How is anyone supposed to remember the CPU cycle steps concisely with three instructions?? Not to mention, I believe this links to at least three subtopics in the OCR specification (1.1.1, 1.1.2, 1.2.1).

This is what it sounds like to answer an exam-paper question on it in class:
"The MDR... copies data from the CIR, to fetch? (yes... no yes👀)
Does this happen in the fetch or decode part of the cycle?
It holds the data before it's written to the main memory, also, when after?
With a jump instruction, that branch technically removes all of the existing instructions and begins a new cycle, so the MDR will be wiped clean anyway. [looks back at the SLR]
Oh, so that's what the MDR does!"

It should be easy. I know what the FDE is meant to do, considering we've gone over it for GCSE, learnt LMC since Year 8, and spent two weeks on FDE recently. I've tried speaking to my teacher about it, revising it over and over every week, and watching videos on it.

In my last SLR, I got a C, and I'm scared of falling behind next week and getting another one since my target is an A.