You can run a simple Qt Quick application using the qmlviewer application, an application provided as part of the Qt SDK. However, most of the time, you'll create a Qt Quick application using the Qt Quick application wizard in Qt Creator, which results in a hybrid application consisting of a Qt C++ application container and QML files as resources that the application loads and plays at runtime.

If we take a look at main.cpp in a project that we create with this wizard, we will see the following code:

#include <QGuiApplication>
#include <QQmlApplicationEngine>

int main(int argc, char *argv[])
{
  QGuiApplication app(argc, argv);

  QQmlApplicationEngine engine;
  engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
  return app.exec();
}

This is pretty straightforward: it creates an instance of QQmlApplicationEngine, a class that inherits from QGuiApplication, and instantiates a top-level window containing a single instance of QQmlEngine, the Qt Quick...