I had the same issue when I first got my iPhone - wanting to know what files are on it, where they are and how I could change things about in it's file structure. It's dead easy really, once you know how.
Download "Diskaid", a freeware iPhone file manager that'll show you everything you need to know, like Finder on a Mac or Windows Explorer, and that also allows you to copy files on to the Phone or on to your Mac or pc from the iPhone. Just google for it and you'll find it comes for both PC and Mac,
good luck, but beware about deleting stuff or changing too much in the Phone's file system, because it can mess it up badly, to the point of having to restore in iTunes,