In the 'textedit' example there is a line - #include "ui_textfinder.h" - wherein a file (ui_textfinder.h) is included that doesn't appear to exist and there is no real explanation of where this came from or where it is, just some vague reference to possibly being auto-generated by uic.
This page of the Qt documentation might answer your question: https://qt-project.org/doc/qt-5.0/qt...a-ui-file.html
In my opinion the documentation of Qt is good (comparing to other libraries).
This tutorial is worth a look as well: http://www.digitalfanatics.org/projects/qt_tutorial/