seeing that applications created with QT claims to run on all platforms, windows, linux, mac....
does the end user require to run or install a plugin ?
or does the applications run natively on each platform....does the end user just install my software and able to run my application fine ??
The end user doesn't need to install a plug-in.
He needs a copy of the qt-library. You can either distribute it as a shared library or you can statically compile it into the application. If you opt for the shared library you can let your installer install that.
You have to compile a binary for each platform you want to deploy your application on. That means you cannot distribute the same application for all platforms.