This is a tutorial to learn KDE programming by examples. It assumes you are working with KDE 4, not KDE 3 (see build_unstable for how to build it).
KDE is tied together with Qt. KDE classes mostly inherit Qt classes and specify them. KDE 4 is based on QT 4, KDE 3 is based on Qt. When this tutorial introduces Qt classes, this helps you learn KDE programming.
Whenever you have a KDE class and want the KDE documentation for it, point your konqueror to kde:KApplication (in case you want help for the class KApplication). For the Qt class QApplication, you can point your konqueror to qt:QApplication.