It's very hard to tell from your question what you already know, so I assume that you:

1. can program


2. in C++


3. with Qt widgets / the QT framework.

As far as I know, the QT Creator is not able to create debian packages to submit to the Ubuntu Software Center.

QT Creator is able to create debian packages for Maemo5 (see here). Looking through the discussions on Maemo, it seemes that this process is not easily changeable, but maybe you can start from there.

If you are not fixated on QT Creator, you can simply use it to create you code and then follow the Ubuntu Packaging Guide to create your debian package.

The actual submission to the Software Center is described here.

For future questions I would suggest you write in more detail what your actual problem is.