You can create the GUI design using QtDesigner and apply functions by coding it using python.
There are many PyQt examples included in this PyQt course, it includes web browser, text editor and many more.
PyQt links the Qt framework, in which many apps are made. You can find a list of apps made with Qt here. Some of the more famous ones are the KDE desktop environment, FileZilla and VLC.
Several web browsers have been made with PyQt, like qutebrowser and Falkon. PyQt includes the blink browser engine.
PyQt has a designer, that lets you design your interface. This makes it very easy to design complex UIs.