Nope. Not at all. You don't. Seriously, no.
You do not need to know where iPhoto stores your photos, or how it organises. Because it's utterly irrelevant. As long as you are making backups of your system using Time Machine or some other backup program, then your iPhoto Library is backed up and you don't have to worry about it.
If you want to avoid accidentally deleting them, then make routine backups and don't muck about in iPhoto's database, because the latter is THE quickest way to lose your photos.
I realise this is a difficult concept for some people to wrap their heads around, but iPhoto is -- well, several things, but at its core it is a database. It stores your originals in a folder called, cunningly, Originals, by time/date/year (if you must know) inside a hidden package. On purpose. To protect them.
If you've modified the photos, then there is a second copy in a folder called -- wait for it -- Modified. Organised the same way. The reason it is not important for you to know any of this is because the thing that a lot of people just don't get is this: anything you want to do to your photos can be done within iPhoto
, completely eliminating the need to do your best to corrupt your own photo library by mucking around with it.
Seriously, name ANYTHING you want to do with your photos (apart from micro-managing where they are -- there's a reason you bought a computer rather than a shoebox, isn't there?) and I'll be happy to tell you how to do it -- it's nearly always incredibly simple (and extra-safe, because Apple designed iPhoto from the ground up to protect your photos).
What happens when you take pictures on your iPhone is this: they are stored on the Camera Roll of your iPhone and, if you've set up Photo Stream properly, a copy of them is delivered to your iPhoto on your Mac.
If you want to "move photos around" in iPhoto, make an album. Choose sort. Sort the album. Done.
If you want to create folders, create albums in iPhoto.
If you want to delete "copies," (do you mean duplicates, perchance?) use a safe third-party program to do this called Duplicate Annihilator
by Brattoo. Costs $8.