I fond it confusing aswell As as for padded bras! I hate them, they're uncomfortable looking. And so are most of the materials
I don't get much choice in style though as I'm a 32F so I'm very limited, but I guess that kind of makes it simple.
I stick to under wired, moulded bras - I find them the most supportive.
As for size, I find googling it always helps. You can find calculators and how to guides and what not. Just google something like 'how to measure my bra size' and maybe add your country if you're finding the sizing is different where you are.