copy below code in FirstQTApp.pro file
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
SOURCES += \
main.cpp
#include <QApplication>
#include <QLabel>
#include <QWidget>
int main(int argc, char *argv[ ])
{
QApplication app(argc, argv);
QLabel hello("This is my First QT Application");
hello.setWindowTitle("First QT App");
hello.resize(400, 400);
hello.show();
return app.exec();
}