There are many great features. Many are really straightforward.
The good starting point is to look at this fast overview and to watch these videos. A PDF version of the KDE style documentation is available as well as an on-line version. Once you have KPhotoAlbum running you should be able to access the documentation under the Help menu using KDE Help Center.
The documentation can always be improved. If you wish to help us don’t hesitate to contact us via IRC or via our mailing list.