I'm just a newbie so I don't have a lot of ground to stand on but from everything I've been reading, this is a huge concept. For starters, malts can be roasted and mashed differently, adding more/less sugars and other fermentables and twisting flavors. As for hops, depending on alpha levels (how much kick it can give) and when you put them in your boil, it can significantly alter flavors, aromas, and overall bitterness.
I've read "the complete homebrew beer book" and there are some good tables inside that tell you what beers and styles certain hops and malts are typically used in.
Meanwhile, I'm taking the mantra that I will learn each as I go. Trial by error and find ones I like. To add yet another twist, I think different yeasts can provide different flavors and finishes of beers. I'm not positive on this though. Good luck with figuring out each one.