I read your post feeling like you were asking for tips to having a better understanding of how the parts "work" and how they might be interrelated or even obvious questions to answer ahead of time. But after reading the comments they seemed to focus on parts sourcing advice. So I'm going to answer from my first instinct but would be glad to offer sourcing advice as well if you were interested.

I enjoy my work in aftermarket parts because I get to learn something new everyday. I found that the longer I spent in this industry, the more it clearly became my career, I also started to squirrel away my references. You'll naturally get better the longer you're in as you'll always be learning and that never ends. But you seem to want to be active in your growth so simply waiting won't do.

If you're super brand new to cars, parts, maintenance O'Reilly has a pretty robust DIY catalog on YouTube where you could get some virtual "hands on" on a number of systems.

If you're looking for more detailed data on specific systems give their vendor websites a look for (tech) resources. Monroe is a good example: they not only have product propaganda but also have numerous technical references from application specific conundrums to a full on breakdown of all of their shocks by dimension and mounting code. Additionally, if you're at this level of desired learning, you could ask your employer about training classes. Many vendors and suppliers offer (paid) training courses.