You do not really need any additional software, though it can make life easier. If you organise your photos into folders on your PC and then sync them with your iPad using iTunes then that folder arrangement will be duplicated in the Photos app on the iPad. However, once those photos are on the iPad you cannot add or delete folders and you cannot delete photos - except by making those changes first of all on the PC and then synching again with the iPad.
If you want to process photos on the iPad then Adobe have some free apps that can help you do most of what you'll probably want to.
Tim