Keyboard navigation in a GUI application might not be the most highlighted feature. Most devices use clickable or touchable controls in the user interface to change screens, open menus or activate buttons. Many developers don't even bother looking at the problem because the customers might not ask for it. But if said application is intended for a device that doesn't have other kind of input, or you have to satisfy some accessibility requirements, it's definitely something that will end up being the feature that blocks a release if it has some known bug.
First we will cover some interesting details of Qt's event system, and then we will move to the details that you should know for providing your UI with a good keyboard navigation system.