Qt Reference materials are available on the Qt Documentation site.
There you will find information on:
- Getting Started with Qt
- Qt Examples and Tutorials
- Qt C++ Classes
- QML Types
- Qt Modules
- Qt Creator
- Qt Licensing
- More comprehensive support documentation
Overview - An overview of why one would use Qt.
Basics - Has links to instructions on how to configure Qt.
FAQs - Has links to the official Qt FAQs.